chronyd.service: Failed to set up mount namespacing: No such file or directory - How to remove temporary files at boot ?

Issue

• The visible issue is that chronyd can't start with this error

  - Subject: Unit chronyd.service has begun start-up
  -- Unit chronyd.service has begun starting up.
  Jul 01 13:20:11 server chronyd[1029]: chronyd version 3.5 starting (+CMDMON +NTP +REFCLOCK +RTC +PRIVDROP +SCFILTER +SIGND +ASYNCDNS +SECHASH +IPV6 +DEBUG)
  Jul 01 13:20:11 server chronyd[1029]: Frequency -45.381 +/- 0.185 ppm read from /var/lib/chrony/drift
  Jul 01 13:20:11 server systemd[1052]: chronyd.service: Failed to set up mount namespacing: No such file or directory
  Jul 01 13:20:11 server systemd[1052]: chronyd.service: Failed at step NAMESPACE spawning /usr/libexec/chrony-helper: No such file or directory ------------------------------> This
  -- Subject: Process /usr/libexec/chrony-helper could not be executed
  -- The process /usr/libexec/chrony-helper could not be executed and failed.
  Jul 01 13:20:11 server systemd[1]: chronyd.service: Control process exited, code=exited status=226
  Jul 01 13:20:11 server chronyd[1029]: chronyd exiting
  Jul 01 13:20:11 server systemd[1]: chronyd.service: Failed with result 'exit-code'.
  -- Subject: Unit chronyd.service has failed
  -- Unit chronyd.service has failed.
  

• A deeper investigation shows an error earlier:

  Jul 07 12:23:17 server systemd[1013]: Applying namespace mount on /run/systemd/unit-root/tmp
  Jul 07 12:23:17 server systemd[1013]: Mount point source '/tmp/systemd-private-c41757ea20594ac384543d9ca7ef9b90-chronyd.service-kVvNYK/tmp' is not accessible: No such file or directory    <<<<--------------
  Jul 07 12:23:17 server systemd[1013]: Failed to mount /tmp/systemd-private-c41757ea20594ac384543d9ca7ef9b90-chronyd.service-kVvNYK/tmp to /run/systemd/unit-root/tmp: No such file or directory <<<-----------
  Jul 07 12:23:17 server systemd[1013]: chronyd.service: Failed to set up mount namespacing: No such file or directory
  Jul 07 12:23:17 server systemd[1013]: chronyd.service: Failed at step NAMESPACE spawning /usr/sbin/chronyd: No such file or directory