I ran into this same issue using 5.1. In the editor everything works fine. In packaged builds the AI movement “rubber bands” on the clients.
I was calling UGameplayStatics::OpenLevel and passing in the host’s IP to join in packaged builds and I was get the rubber band movement on AI controlled characters.
If I use the OnlineSubsystems (I have only tested Steam) the problem goes away and the AI controlled characters move as intended. In the long run this works for my particular situation by does slow down the development process.