The loose round issue isn't unique to the P938. All my pistols have done it at one time or another. And some rifles. If it's magazine fed it can happen.
The slide/bolt depresses the next round, it's lower than the feed lips. Dropping the mag allows it to pop up and it will hit the lips, which aren't designed to be a controlled feed - they are just there to hold the round when it's static, not dynamic. The slide/bolt often can strip the cartridge off and chamber it before the stack of rounds can overcome it's own inertia and rise. In some cases a really fast cycle can override the next round before it even has a chance to come up. Proper timing has to slow the action enough to let the next round up all the way.
Works just fine at speed, it's hand cycling it's not optimized to deal with. You generally can't have both. The P938 has a stiff mag spring, the better cure is a mag loader. Much easier to deal with them if you shoot it a lot. If it's a carry piece, tho, then unloading it isn't very frequent.