Errors only appear as events

We are having a problem that many of our errors are appearing only as events, not as errors in sentry. What I mean by that: every error can be found under “Discover” → “Events” section, but not in “issues” section.

Basically in every event, which doesn’t have an issue, we see: “The linked issue cannot be found. It may have been deleted, or merged.”. We know no one tampered with it… Also this is not constant, as some issues appear normally

The interesting thing is next to all of those events, we see, that those are tagged as handled: true. Maybe this has something to do with it?

PHP 7.4
Sentry on premesis: Sentry 20
SDK: latest 3.7
Symfony bundle: 4.1

Where to start?
Any ideas are welcomed