Telegram receiver stoped working

Ok, so my telegram receiver stopped receiving "all" chat messages.
I do know, it received the messages at some point.

But for now, it only receives messages starting with an "/".

This is described in the following threads:
https://discourse.nodered.org/t/telegram-receiver-stops-working/41796/7
https://discourse.nodered.org/t/telegram-receiver-receives-only-messages-starting-with/41412

But they're closed and I didn't find a solution in them, exccept the answer that it should be a problem with my bot settings or/and an update. But I'm already using node-red-contrib-telegrambot v11.2.0.

Could anyone give me a hint, what settings could be wrong?

Does it start working again if you restart node-red?

Nope, it doesn't.

Did you change anything in your flows, group or bot settings - that you can remember?

No, i didn't change anything I am aware of.

But I found something in the settings:
Bots: An introduction for developers (telegram.org)
So I checked, and my Bot was in privacy mode. I don't know why some messages get through. It might be, I messed something up with the identifiers, so these messages were more answers than new messages.