We have a logical replication set up (pg 13) with publication <> subscription. All good, most of the time.

But every two weeks or so I get a notification (internal replication monitoring) that the replication is ‘out of sync’ with the underlying message that there is no subscription on the receiving machine. As far as I can see there is no event that can be linked to this. And it is not being remove manually.

What reasons could there be for this?