No OTA update Lineage OS 15.1

Hi there,
I needed to update TWRP for the LOS 14.1 --> 15.1 Upgrade.
Now I get the message that an update to LOS 15.1 20.08.2018 is available, but trying to update I’m getting the message:

“Hinweis: Diese Funktion erfordert ein kompatibles Recovery-System, anderenfalls muss das Update manuell installiert werden.”

which seems to be a TWRP thing. I darkly remember there’s an adapted TWRP for LOS OTA updates to prevent overwriting something?

What can I do?
Thanks in advance

A post was merged into an existing topic: Upgrading from official 14.1 to 15.1 (feedback/issues)