Sometimes when switching slides problems occur. It could be tolerances, that the new slide is catching on somewhere or needs some braking in.
Also it could be that the mos slide is heavier, especially with a red dot mounted, than the original slide.
Then you migh need to find the correct recoil spring. Too weak and it won’t return to battery. But too strong will make it hard for the slide to lock back.
I think you have to experiment a bit.
I doubt a new frame will solve your problem.
edit: Is it a steel mos slide? That would explain a lot