I’ve not had this issue on my Clara (yet?) but Mike Hall has your rundown on what to do if suddenly you don’t seem to be able to read DRM-protected ebooks on your Kobo, the tl;dr of which appears to be to ignore the advice and factory reset your device.
Bix dot Blog
The unsupported use case of Bix Frankonis’ disordered, surplus, mediocre midlife in St. Johns, Oregon.
No fear, no hate, no thoughtless bullshit, and no nazis.