Do not use AUTOMATIC video quality.
I have been having the same issue as a lot of others on here. I try to export only to have it fail and say "something went wrong", UNTIL I started changing the video quality to 1080 match frame rate.
This is the setting above the "EXPORT" button right before the video starts rendering. It is set (as a default) to automatic, i changed it and my vids now export without errors. Hope this helps you, and adobe hopefully you can fix the bug.
I appreciate you writing in with this suggestion. We’re aware of the stability issues during export on iOS. We’re actively working on improving the performance.