The bug
Using the /summon command to summon a turtle with a passenger (Illagers) with the Passengers tag while the turtle's body interacts with watch causes the game to crash.
How to reproduce
1. Summon turtle with the Passengers tag. (Passenger should only be illagers.)
/summon turtle ~ ~ ~ {Passengers:[{id:vindicator}]}2. Place water
3. The turtle is "trying" to swim in water, thus making the game crash.
Thank you for your report!
We're actually already tracking this issue in MC-158484, so I resolved and linked this ticket as a duplicate.
If you would like to add a vote and any extra information to the main ticket it would be appreciated.
If you haven't already, you might like to make use of the search feature in the future to see if the issue has already been reported.