OK, since no one answered, I figured this was something specific to my setup so I looked into it a bit more. And I believe I found the culprit!
I have OmniPresence on my desktop Mac and also on my MacBook and I have backups to both on the same external drive, on different partitions. I hadn’t updated OmniPresence on the MacBook for a while because I wasn’t using it much during the Covid lockdown and even in the few months before that. So on my Mac I had version 1.7 and there was a 1.6 version on the backup of the MacBook.
Every morning, when I turn on the Mac, all the partitions on the external disk are also mounted for the morning backup. So, I suppose that sometimes, OmniPresence 1.6 from the MacBook backup was automatically launched, sometimes it was the 1.7 version on my Mac. When it was a different one from last time, the release notes appeared, the system probably thinking it was something new. At that time, I had another problem and it didn’t occur to me that the two were related but now I realize that they were. When the backup was done and I wanted to unmount the partitions on the external disk, it sometimes didn’t go well. I had to force eject the MacBook backup partition and this could cause a kernel panic.
The solution I found was to update OmniPresence on the MacBook and do a backup to the external disk. Now it’s version 1.7 everywhere. I suppose it is now always the version on my Mac that launches because, since the update, I don’t see the release notes anymore and the partitions eject just fine.
Hopefully, this may one day be of use to someone else.