[bazookajoe]

Welcome to hell! Lol.

This is the exact behaviour I have with OTG SD/USB storage on Android 10+ devices. Ordinarily not an issue because most of my devices have external SD slots and CC works fine with them but my Onyx Leaf does not and my library is bigger than internal storage. So that's a whole problem I've recently ran into myself right down to every aspect of the behaviour you're experiencing, which has then forced me to look at how my other Android devices respond with OTG (10, 11, 12 not well. At all. Pie was the last time it was flawless).

I'm sorry, I don't know anything about Chromebooks I'm an idiot and cannot help you technically however, maybe you could look into how Chromebooks handle external storage. Is formatting it as adoptable storage an option? Mounting scripts? Things I'm too stupid to comprehend? I say this because I think you might have to go outside the CC thread on this one to bigger things like Chrome O/S, storage scope etc, because it may (and I say may) be a more broadly systemic issue for you too and not just the CC app. Obviously you're not explicitly OTG (or are you?) but it makes me suspicious given we're identical in result which makes me think that there's just something going on there with your storage. It's nothing I can find much info on at all.

For me personally I've torn my hair out over this for weeks. Root hasn't worked, chmodding, permission changes, 2 different Magisk modules haven't and about 7 different apps haven't worked. It isn't just restricted to CC either, so it's not just that it's an old/outdated program (though CC is certainly that). The only real success I've had is with Paragon exFAT/NTFS making ReadEra finally detect the OTG SD. That's it. The closest I've come to minor change from your default behaviour in CC is with extSD in Magisk but I still have it unable to open the file, says it's missing just like you except this is the only time it can tell what size the file is. Otherwise default behaviour says the file is size: 0 in the "Book Detials" view. Still can't open books though :/

I guess one way to see if it's a systemic issue is to try other apps and see if you suffer storage restrictions similar to what I've experienced. As mentioned, ReadEra couldn't read OTG storage at all without explicit mounting app, I could select it, but it would not read it, an app I use that usually allows external storage is Smart Audiobook Player and that can't access external. Calibre Sync displays similar behaviour to CC in that it will download but not read (though since Leaf updating firmware things have gotten more restricted to what download folders I can choose).

If I make any headway I'll update here (or somewhere else relevant) for future people. Good luck.