Alpha Untamed

There may have been a change in the file path or programming behind horses, mules, and llamas in order to allow wandering villagers to exist. That could be what's causing that, and if that's the case, then all you can do is find out how to update the texture pack to accomodate for it.

It's the resource pack, I presume. If you have any screenshots where you're not using a resource pack and are still having this issue, then it's likely something going on in the game itself. If you disable the resource pack and it's still happening, I'd suggest uninstalling then reinstalling the game.

I believe that this is simply an issue with WiFi. I can't see it being due to your NAT type, unless it's possibly a cross-play issue. Are you both on Xbox One? If so, check your WiFi speed.

I would personally try uninstalling, then reinstalling the app. It may have something to do with something going on internally. This does mean that he'd lose his worlds, but I don't believe I see any other alternative.

I believe this is actually intended behavior. In order to move down in water, you crouch. Thus, it's completely expected that the shield activated while moving down in water.