Oh no, that's weird. Would you mind trying a few files in quick succession, then sending me a log file? You can find the log files in Settings => About => Show log file, then you can for example tap "Share", and send it to yourself in an e-mail or something, then upload it here (or send it directly to my e-mail if you wish,
erlend.dahl@gmail.com). Hopefully the .error.txt file from today contains what I need, but you could also send the .debug.txt file if you want. There shouldn't be any personal information in any of them, but there could be filenames and titles from your books.
Sorry about that, and thank you so much for your patience so far!