What frustrates me is that it looks like it works, but once in a while it breaks in a way that is pretty much irreparable (or at least not in a practical way).
I want to run an iOS/Android app that backs up images on my server. I tried the iOS app and when it works, it's cool. It's just that once in a while I get errors like "locked webdav" files and it never seems to recover, or sometimes it just stops synchronising and the only way to recover seems to be to restart the sync from zero. It will gladly upload 80GB of pictures "for nothing", discarding each one when it arrives on the server because it already exists (or so it seems, maybe it just overwrites everything).
The thing is that I want my family to use the app, so I can't access their phone for multiple hours every 2 weeks; it has to work reliably.
If it was just for backing up my photos... well I don't need Nextcloud for that.
Again, alternatives just don't seem to exist, where I can install an app on my parent's iOS and have it synchronise their photo gallery in the background. Except I guess iCloud, that is.