lazy arm in fly

[Mozla]

:wave:
What is the cure for a lazy arm in fly, always the right that seems to bend more and lag behind the other? No shoulder or arm problems identified!

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id go straight back to basics, and practice it in front of a mirror, and also walking and doing it in the water.
Try to feel it in the shoulders and all the way down in the wrist, this will contract your arms and should bring them together at the same time.
Start slow and then build up the speed when you feel more comfortable.