More in this thread below, but starting a dedicated one here to draw more attention to it. A number of things break in the 3.0 update - all sideloaded content breaks and won't open throwing a "remove and re-add your books" error. If a mod could merge the last few posts from below to this new thread that'd be great!
See here:
https://www.mobileread.com/forums/sho...11#post2006611
Done, Dale