Maybe it could be something else, but IME, this is caused by insufficient Steem bandwidth. If you encounter that error, leave the upload page open. Take a look at https://steemd.com/@mobilechaos to see what your used and available bandwidth is (on the left side). If you're over the limit, it will say "recharging". Then you will have to wait until you have enough (this goes for other posts and comments you try to make, too). You can try submitting again later without closing the upload page.

One thing I've found that exacerbates the problem is when you edit video info on a DTube page, and you click the "Edit ✓" button to submit it, there is (last time I checked) absolutely no feedback. So even if it's successful, it looks like it didn't work, and you might try clicking it again. This can cause multiple edits in the blockchain, eating up your bandwidth more than necessary. I hope they fix it.