I got a coredump when testing with the REL_14_STABLE branch, which is as below:
I noticed that in commit 10520f4346876aad4941797c2255a21bdac74739, int delayChkpt has been changed back to bool delayChkpt + bool delayChkptEnd. However, the initialization to delayChkptEnd is missed in functionInitProcess. When autovacuum_proc1 is in RelationTruncate, the delayChkptEnd will be set as true. If autovacuum_proc1 receives a cancel signal and handles it at this time, autovacuum_proc1 will exit without reseting delayChkptEnd in its error handling process. After that, if autovacuum_proc2 reuses this PGPROC structure, the above error will occur.
I add a patch to fix this bug in the attachment, hope you can check it.