It could be about your phone browser's memory or access to other system resources. The android default file browser/picker seems to only handle fairly small files for some reason.
SE Explorer and MIXplorer seem to handle it a lot better but it can be a bit screwy at times too.
Sometimes it's the file itself not wanting to play with the server that it's being sent to. This can be mitigated my converting the file.
Best bet? Try on a PC. If that fails then convert and try again. Otherwise on your phone use Firefox, MiXplorer but stay on that page, don't change to a different app, and don't let your screen turn off (painful, I know).
If you just want the video up on TT and it's not working for you, let me know the file and I'll upload it on one of my channels and I can credit you for it if that is a workable solution for you. **Edit:**There's a capacity for ownership changes on TT I forgot about too. I'd be able to try that out and pass the video over to your account as well.