I have run into this once with Muse HD (build 2538). I was on trip, no computer anywhere. I just powered it off and then back on and all was well.
My recent addition was an e-book I downloaded from an on-line shop (Elisa Kirja:
https://www.elisa.fi/kirja). I haven't removed that addition or done any other changes in the e-readers library, it has been working fine.