Newest version (android Samsung Ultra) doesn't save videos in gallery until reboot

At least part of what you’re describing has apparently been reported with the v3.1 RC and production app (at this time there is apparently no release announcement, though there is a Release Notes mention), starting here:

Since you’ve already rolled back to an earlier app version and disabled automatic updates, then I guess the thing to do is probably report it in (a) relevant topic(s) and wait for an update. If you were still on the v3.1.0 Android app, then I’d recommend logging it and opening a Support ticket.