I noticed that i am only able to upload videos that are under 10mb.
I am using Nextcloud 12.0.2 and an iPhone 6S with iOS 11.
Autoupload does not work and manual upload does not work.
Well, one thing I just realized is since you and I are on iOS 11, all our photos are going to get synced to Nextcloud as .heic files, which, I have nothing that can open 
Maybe this helps though, I found that I had to enable permissions for Nextcloud on iOS again
I was able to upload files as jpg just fine. I did have to grant permissions again, but still not able to upload videos.
Are you certain that the settings didn’t change for video upload on the client? I guess the next thing to test is can you upload any other file that is greater than 10mb right now?
I just uploaded a file that was 290 MB just fine.
It is really odd that it doesn’t want to take the files.
I finally kept trying and was able to finally upload the files. I had to do them one at a time multiple times and they finally loaded. They are not even that big ~30 MB.
Hmmm. I am a bit at a loss. The most I can say is I’m on 12.0.3 beta right now and I’m not experiencing this issue. Perhaps it won’t be an issue when that release is officially out?
Also having the same issue with iOS 11.0 and NextCloud 12.0.3. Photos (HEIC) upload fine, but I can’t get video (HVEC) to upload. They try to upload but fail with only 0 bytes or ~20KB unreadable file placeholders.