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What is your set for the OHS like?
Your shoulder/arm may be in an ineffective position which is impacting the weigh you are able to use.
OHS is a complex movement that highlights other areas as well.
It pulls in midline stability and maintaining a stable position with movement.
The ROM issue with the shoulder are an impacting factor.
It doesn’t sound like the strengthening exercises you are hitting the area(s) that need attention.
When doing OHS are your arm pits forward and elbow pit facing up?
Have you hit anything with your t spine?