SS issues AP5

Took it out of another working platform, in my AP5 with 3d lower however doesn’t seem to function in SS. Works perfect in semi and safe. In SS does one or 2 shots then dead trigger and light primer strikes. With upper not attached, I polished the trigger and it functions perfect while pulling the lever back, the trigger resets as it should. But when attaching the upper and metal trip, it does not reset unless I let off the trigger slightly.