I had a flow that worked flawlessly for a while, and then it began to issue errors like the ones on the image. I have no clue, where to continue debugging. All tasks succeed, but the flow becomes failed because of these messages. Any hints are appreciated. I have already restarted Prefect server and the agent.

Hey @Andor Tóth, from experience, something corrupted the registration. Could you try re-registering and re-running?

I am just on that. A few seconds, and it turns out...

How big is this flow? Over 1k tasks? Not mapped tasks. Talking about unique tasks

ah, that did the trick