Update to 21.0.9. From the release announcements:

  --- POTENTIAL INCOMPATIBILITIES -------------------------------------

  OTP-15225    Application(s): erts

                Fixed a bug causing some Erlang references to be
                inconsistently ordered. This could for example cause
                failure to look up certain elements with references as
                keys in search data structures. This bug was introduced
                in R13B02.

                Thanks to Simon Cornish for finding the bug and
                supplying a fix.

  --- compiler-7.2.4 --------------------------------------------------

  --- Fixed Bugs and Malfunctions ---

  OTP-15292    Application(s): compiler

                Fix a regression in OTP-15204 that removed .beam file
                metadata that some external build tools relied on.

  OTP-15204    Application(s): compiler
                Related Id(s): ERL-679

                Fixed an issue where files compiled with the
                +deterministic option differed if they were compiled in
                a different directory but were otherwise identical.

  OTP-15156    Application(s): compiler
              Related Id(s): ERL-655

              In rare cases involving matching of binary literal
              strings, the compiler could optimize away code that
              should be executed.

  OTP-15157    Application(s): compiler

              There could be an internal consistency check failure
              when compiling code that called map_get(Key, Map) and
              then updated the same map.

  OTP-15166    Application(s): compiler
              Related Id(s): ERL-660

              In rare circumstances, the compiler could crash in
              beam_jump when compiling a floating point operation.

  OTP-15150    Application(s): compiler
              Related Id(s): ERL-650

              The compiler could could crash when compiling a
              complicated function that used the binary syntax.

  Full runtime dependencies of compiler-7.2.4: crypto-3.6, erts-9.0,
  hipe-3.12, kernel-4.0, stdlib-2.5

  --- erts-10.0.8 -----------------------------------------------------

  --- Fixed Bugs and Malfunctions ---

  OTP-15289    Application(s): erts
                Related Id(s): ERIERL-235, ERL-576, OTP-14943

                As of ERTS version 10.0 (OTP 21.0) the erl_child_setup
                program, which creates port programs, ignores TERM
                signals. This setting was unintentionally inherited by
                port programs. Handling of TERM signals in port
                programs has now been restored to the default behavior.
                That is, terminate the process.

  OTP-15296    Application(s): erts
                Related Id(s): ERIERL-226, OTP-15279

                The fix made for OTP-15279 in erts-10.07 (OTP-21.0.8)
                was not complete. It could cause a new connection
                attempt to be incorrectly aborted in certain cases.
                This fix will amend that flaw.

  OTP-15275    Application(s): erts
                Related Id(s): PR-1943

                A process could get stuck in an infinite rescheduling
                loop between normal and dirty schedulers. This bug was
                introduced in ERTS version 10.0.

                Thanks to Maxim Fedorov for finding and fixing this
                issue.

  OTP-15279    Application(s): erts
                Related Id(s): ERIERL-226

                Garbage collection of a distribution entry could cause
                an emulator crash if net_kernel had not brought
                previous connection attempts on it down properly.

  OTP-15237    Application(s): erts

                A race between termination of a process and resume of
                the same process via erlang:resume_process/1 could
                cause the VM to crash. This bug was introduced in erts
                version 10.0 (OTP 21.0).

  OTP-15269    Application(s): erts
                Related Id(s): ERL-713

                When tracing on running, in trace events could be lost
                when a process was rescheduled between a dirty and a
                normal scheduler.

  OTP-15223    Application(s): erts

                Fixed a bug which caused an emulator crash when
                enif_send() was called by a NIF that executed on a
                dirty scheduler. The bug was either triggered when the
                NIF called enif_send() without a message environment,
                or when the process executing the NIF was send traced.

  OTP-15225    Application(s): erts

                *** POTENTIAL INCOMPATIBILITY ***

                Fixed a bug causing some Erlang references to be
                inconsistently ordered. This could for example cause
                failure to look up certain elements with references as
                keys in search data structures. This bug was introduced
                in R13B02.

                Thanks to Simon Cornish for finding the bug and
                supplying a fix.

  OTP-15169    Application(s): erts

              Fixed a bug that prevented the noshell option from
              working correctly on Mac OS X and BSD.

  OTP-15184    Application(s): erts

              Fixed a crash when matching directly against a literal
              map using a single key that had been saved on the
              stack.

  OTP-15196    Application(s): erts

              Fix node crash when passing a bad time option to
              file:read_file_info/2.

  OTP-15154    Application(s): erts

                Fixed a scheduler bug that caused normal schedulers to
                run dirty code.

  OTP-15183    Application(s): erts
                Related Id(s): ERL-670

                Fixed a bug in erlang:trace_info/2 which caused the
                emulator to crash when a bad argument was passed. The
                bug was introduced in ERTS version 10.0.

  OTP-15067    Application(s): erts
              Related Id(s): ERL-573

              Fixed a rare bug that could cause processes to be
              scheduled after they had been freed.

  OTP-15158    Application(s): erts
              Related Id(s): ERL-654

              Fixed a race condition in the inet driver that could
              cause receive to hang when the emulator was compiled
              with gcc 8.

  OTP-15147    Application(s): erts
              Related Id(s): ERL-644

              The keys used in os:getenv and os:putenv are
              case-insensitive again on Windows.

  Full runtime dependencies of erts-10.0.8: kernel-6.0, sasl-3.0.1,
  stdlib-3.5

  --- kernel-6.0.1 ----------------------------------------------------

  --- Fixed Bugs and Malfunctions ---

  OTP-15280    Application(s): kernel
                Related Id(s): ERIERL-226, OTP-15279

                Fixed bug in net_kernel that could cause an emulator
                crash if certain connection attempts failed. Bug exists
                since kernel-6.0 (OTP-21.0).

  Full runtime dependencies of kernel-6.0.1: erts-10.0, sasl-3.0,
  stdlib-3.5

--- crypto-4.3.2 ----------------------------------------------------

--- Fixed Bugs and Malfunctions ---

  OTP-15233    Application(s): crypto

              Update the crypto engine functions to handle multiple
              loads of an engine.

              engine_load/3/4 is updated so it doesn't add the engine
              ID to OpenSSLs internal list of engines which makes it
              possible to run the engine_load more than once if it
              doesn't contain global data.

              Added ensure_engine_loaded/2/3 which guarantees that
              the engine just is loaded once and the following calls
              just returns a reference to it. This is done by add the
              ID to the internal OpenSSL list and check if it is
              already registered when the function is called.

              Added ensure_engine_unloaded/1/2 to unload engines
              loaded with ensure_engine_loaded.

              Then some more utility functions are added.

              engine_add/1, adds the engine to OpenSSL internal list

              engine_remove/1, remove the engine from OpenSSL
              internal list

              engine_get_id/1, fetch the engines id

              engine_get_name/1, fetch the engine name

  OTP-15194    Application(s): crypto
                Related Id(s): ERL-673

                Fixed a node crash in crypto:compute_key(ecdh, ...)
                when passing a wrongly typed Others argument.

Full runtime dependencies of crypto-4.3.2: erts-9.0, kernel-5.3,
stdlib-3.4

--- public_key-1.6.1 ------------------------------------------------

  OTP-15151    Application(s): public_key
              Related Id(s): OTP-15113

              Some of the keylengths in the newly generated moduli
              file in public_key are not universally supported. This
              could cause the SSH key exchange
              diffie-hellman-group-exchange-sha* to fail.

              Those keylengths are now removed.

Full runtime dependencies of public_key-1.6.1: asn1-3.0, crypto-3.8,
erts-6.0, kernel-3.0, stdlib-3.5

--- stdlib-3.5.1 ----------------------------------------------------

  OTP-15159    Application(s): stdlib

              Fix a bug that could cause a crash when formatting a
              list of non-characters using the control sequences p or
              P and limiting the output with the option chars_limit.

Full runtime dependencies of stdlib-3.5.1: compiler-5.0, crypto-3.3,
erts-10.0, kernel-6.0, sasl-3.0

(schmonz)