Default Weird ext sd card issues

Hey guys.

Since I got my M8 I have had all sort of weird issues with the ext sd card.

For example, I have the camera app save photos to the ext card, and all seems to be fine. I can view the photos immediately, delete them, edit them etc.
However, after a few days, some of them start becoming unreadable and inaccessible, some just disappear.

Another example is Spotify. I have it download music for offline availability, and all seems fine for the moment, I can play some files offline, but everytime I re-open the app, I always get some missing files that spotify has to re-download. This is a good situation, as sometimes, when I open the app, it behaves just like it is the first time I use it, and I have to sign in and re-download everything.

Also, when some apps update, they automatically move to the ext sd card. After a restart, they become unavailable. To fix this, I have to re-install the app, and immediately move the apps back to the internal sd card.

I have tried 3 different cards, all 32GB UH1.

Please note that before the M8, I had an S4 and I had no such problems.

This is really annoying. Can someone please help me out here?

Thank you in advance!
Current: HTC One M8 (Gunmetal) + Spigen Slim Armor (Gunmetal)
ViperOne - ElementalX - Firewater S-Off(ed)
Old: HTC One * Galaxy S4 (I9505) * Galaxy S3 (I9300) * Galaxy S3 LTE (I9305) * Galaxy S (I9000)