Really no where near enough information to give you a terribly specific answer, but here is a general.
The twist is perfectly fine for the 50gr bullet, and heavier; UNLESS you are pushing them so slow, that they can't stabilize.
Without knowing that load(mostly speed) it is impossible to tell.
Barrels will always have preferences, certainly possible that yours hasn't been fed it's "happy load", or that it just doesn't like them.