This happens often when something I'm riding goes invisible such as horses or boats. 

What I expected to happen was...:
Pressing shift causes me to jump off and I can see my transport

What actually happened was...:
I jumped off and I couldn't. Horses go invisible and boats too accept the last one if they go invisible I'll also start glitching and shaking in the water while walking slow. 

Steps to Reproduce:
1. Ride a transport thing
2. Press shift
3. Probably gone invisible

It doesn't happen all the time but often enough that it's annoying. The way I learnt to deal with it was to exit world and enter again then I'll be able to see them but not a fan of doing this all the time it happens. I found some forums where a couple dozen other people were having the same problem. I don't know why it does it sometimes but not others.

Hope you can fix it!

Thank!