When taking a picture or video with Samsung Galaxy S5 running LineageOS (Android 7), they will show up in the uploads list of the Nextcloud app, but you have to push them manually again after they failed the first time (which they always do).
I yesterday installed the newest app using F-Droid, but things are still the same.
I even have some large videos, which will not upload at all, they start and then abort with an error message.
Same time the problem does not exist on another Android 6.0 phone.
Can I help you with some information to resolve this?