Ost pios were never supposed to have 100% moving accuracy, so it was a bugfix.
CEs on the other hand got a plain nerf.
Apparently conscripts are in such a deep shit that even CEs outperformed them.
Then the change to combat engineers can be seen as bug fix too. It changed because last patch they altered conscripts in a way that the mosin nagant was better but that conscripts had more increased received accuracy. Since combat engineers use the same weapon as conscripts they got buffed as well but without the increased received accuracy penalty.
Now they changed that engineers have the prepre patch mosin back I think