Gitea 1.8.1 startup problem with issue indexer error


two days ago gitea 1.8.1 stopped running (on a NanoPC T4 with Armbian Stretch) and on every restart I am getting the following error message:

[...itea/routers/init.go:95 GlobalInit()] [E] Failed to initialize issue indexer: leveldb: manifest corrupted (field 'comparer'): missing [file=MANIFEST-000042]

I am using the default issue indexer, and the system wasn’t used in the last 5 days and was simply running in the background. Upgrade from 1.8.0 happened on May 8th and until 2 days ago gitea worked flawlessly.

Any hints/ideas what I could try?