While uploading a large number of photos and videos from my iPhone Photos to Camera Uploads in by Dropbox, I noticed the notification icon on the Dropbox iOS app was stuck at some large number. This occurred after the phone locked itself. I exited the app and restarted it. Still stuck.
Turns out, one of the video files wasn't able to upload before the lock timeout expired. When this happens the Dropbox app runs for a short while then iOS prevents it from running the file upload in the background.
- Disable screen lock, then just wait.
- Cancel the large file upload that is stuck
Go to the Camera Uploads folder, find other stuck files and cancel all of the remaining uploads.