I just checked my manual and 120 grain lead at 1.065, 4.1 grains is a max load. Your load is longer but 5 grains heavier in boolit weight. Minimum load is 3.0 grains. I’d drop the load to 3.2 grains and increase the powder charge until you get functioning slide lock back. Don’t change the powder yet. Try .357 within the 3.2 to 3.9 grains. Then .358 with the same loads.