Tvheadend

Tvheadend (4.3.0~pre) simply refuses to record as I tell it to, for no apparent reason. As an example, I have an autorec set up with the following settings:

Title: Taskmaster
Channel: Channel 4 HD
Duplicate handling: All
Priority: High

All other settings are default (i.e. no other restrictions). When I check the upcoming recordings, the Thursday night broadcast is always listed, as expected. However, it usually doesn't record. At some point during the Thursday it just disappears from the upcoming recordings list for no apparent reason.

This has been going on for years and previous attempts to get help have led nowhere. However, I now have a bit more information based on debug and trace logging. It looks like an EPG grab is triggered (not sure why since it doesn't match the cron schedule I have for EPG grabs), then the recording is purged due to "No broadcast matched when entry was reloaded from dvr/log" according to the source comments:

2022-06-16 13:41:21.678 [   INFO]:epgdb: snapshot start
...
2022-06-16 13:43:16.763 [   INFO]:dvr: PURGE: No broadcast matched when entry was reloaded from dvr/log
2022-06-16 13:43:16.763 [   INFO]:dvr: Entry d28e4cea565de268f5c5a1ec55e6c893 can be purged for "New: Taskmaster" start 2022-06-16;21:00:00(+0100) stop 2022-06-16;22:00:00(+0100)

Why is the broadcast being purged before the recording happens? Why would tvheadend think there's no matched entry in the EPG when it's clearly there? Note that some of the purged recordings did actually happen, so they must have been re-added at some point, maybe during another EPG update? I wonder if there's some issue with the EPG update not fully populating the EPG before the Purging obsolete autorec entries for current schedule part of the code is run?