There are a lot of things that can be happening during slide movement and the force of recoil, so just the simple fact that it locks back manually with an empty mag doesn't quite rule out gun issues, although I agree it is a good function test. We now know that statically, the slide lever functions as designed.
After ensuring the weapon is clear, Do the following:
- Remove the magazine and slide. With the frame in your hand, push up on the left slide release lever. Does it spring back when you let off? How much resistance do you feel when you push up? This will be subjective of course, but humor me. Is the resistance more than you would expect, about what you would expect, or less than you would expect?
- With slide off, insert a magazine now and pay special attention to the movement of the left lever. Did it appear to move freely and smoothly? With the mag inserted, and the lever pushed up by the follower, try to push up even further. Is there any more room for the lever to move up? For reference, my follower pushes the lever up until it can't move any further. Push the lever down. Does it seem to move freely?
- Remove the mag and pay special attention to the lever and look for any irregularities or inconsistencies in movement.
- Look down into the magwell and watch as you slide the mag into the gun. Pay special attention to the relationship of the follower and the part of the slide release lever where they make contact. Are there any irregularities or inconsistencies in the way that the follower moves in relation to the arm on the slide release lever when they make contact? Release mag and reinsert several times and take note of anything that doesn't seem right.
- If feasible, find someone with a P30 and do the above steps side by side with your gun. If all else fails, go to a gun store and see if someone has a P30 in stock that you can "take a look at".
Report back when you have a chance.