I had to leave the world and rejoin to see the donkey again.
Environment
Multiplayer riding donkey, got off and it dissappeared to me but to other players it was still there.
Linked issues
duplicates 1
Comments 2
Thank you for your report!
We're actually already tracking this issue in MC-101247, 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.
I have also had this occur on my 1.14.4 world.