Yes the safety/decocker also engages the semi/auto function so it must be stuck in the medium position.
Yep that's the same gap I have on my 2 mags which both lock the slide properly.
1) With no magazine, pull back the slide and hold it. When you push up on the slide catch does it move freely up and down?
2) With a mag in, pull the slide back. Does it always catch?
- If it doesn't then something is stopping it moving.
- If it does lock when manually pulled then the slide is not moving back far enough when fired. There are several possible reasons for this so further investigation would be required.