devtrackers.gg
Happened to me once or twice.
For some reason the packet that said you used grappler doesn't reach the server, but the client thinks it did. It tries to predict that you're being pulled to the ball, but then comes the packet from the server with your actual position. The client pulls you forward and server pushes you back. At least on your screen.
If you'd watched the replay you'd see that when you're supposed to have used the grappler nothing happened and was standing still.
It's pretty rare and I don't know if it's purely network's fault or if it's an actual game bug but I'll try shouting at u/Psyonix_Devin