When I play online multiplayer with my friends, who also play on Switch, we encounter an issue when riding horses or sometimes boats.

Basically, when you dismount a horse, sometimes it gets stuck in the jump animation (no matter what you were doing, jumping or not) and you cannot remount the horse. When you try, it opens the inventory instead.

Additionally, if you try to ride something else, like a boat, it teleports you back onto the horse you dismounted from.

The last time this happened, it teleported me onto the horse and the horse was spinning around in the jump animation and my character wasn't even in the saddle.