[SOLVED] Self-hosted NTFY does not receive all notifications

I do POSTs from a backend app to a self-hosted ntfy instance (docker). The POSTs do not fail and I also save them in local db. I now compare the notifications cached in /var/cache/ntfy/cache.db against the ones I save in my local db and I see that ntfy is missing a lot. As an example, today for example I have POSTed 540 times and in cache.db I see only 60 of them. The skipped ones are not even at regular intervals.

Is there a logfile I can check in the ntfy service? The output of the ntfy process itself only shows the expected INFO Server stats... message but not errors.

Is there any reason ntfy may not be registering some of the POSTed notifications?

Best regards.

Edit: I can also confirm on the mobile app that I did not receive the skipped ones; I have only received indeed the ones that I see in ntfy's cache.db.