Thanks for testing the nightly. Also see
https://github.com/koreader/koreader/issues/8401
You can grab the older nightly from
http://build.koreader.rocks/download...b1_2021-10-31/ (or the 2021.10 stable; I don't think we've had any data format changes?) and overwrite your directory. Alternatively you can wait a day or two and do the same with the new nightly fixed by @NiLuJe, assuming he has time.