Its pretty apparent this ended up being the issue.
Filed it down and I believe its fine now, but have yet to go and try some 147s through it.
During feeding the rounds could hit and push up the slide stop due to the 147s profile.
I hand stripped rounds, and generally when it would lock the gun open prematurely, near the end of a mag, it would bounce the SS all the way to the other side.
Im not sure why it was so far inward, it didn't need half of that material to engage the follower of the magazine.