I purchased an M&P compact a few months ago. I have fired over 500 rounds through it with no issues. I went to the range two weeks ago after a couple of magazines the gun started to not eject the spent round. I looked the gun over and everything looked fine. It was hot that day and I thought some of my sweat might have gotten in to the slide and was causing the gun not to eject properly. I went home cleaned and oiled the gun. Last weekend I went back to the range and had the same issue. This time I was prepared with a rag and gun oil. I cleaned the slides off and applied oil. It shot great for about 30 rounds and started doing it again. I am using Winchester Super X ammo and have shot over 1000 rounds with no issues. Any suggestions?

Clean your 22C again and when you're done, take a very close look in the chamber. I bet you'll find it needs a better scrubbing. This is exactly what I was experiencing early on with my 22C. I found that I need to run the bronze brush through the chamber and scrub with solvent much longer than I do with any of my centerfire pistols. Even with a spotless pistol, I find most ammo will start to get stuck in the chamber after 75-100 rounds. Winchester, Federal and Remington Thunderjunk seem to be the worst but CCI will run reliably much longer than I can so I've never seen this happen with them.

My wife has a 22c for about 3 years now. In that time she has put several thousand rounds down range. We have found that it is somewhat picky about what kind of ammo it likes. Standard velocity can be problematic so we only use only high velocity ammo now. It works flawlessly with any high velocity we've tried except Federal Automatch. We usually stick with 40gr Mini Mags, but Aguila, Fiocchi, Sellier and Belloit, and even Remington Golden Bullets cycle without issue.

We clean and lube it ( generously ) after each range visit.

Remington Thunderbolts have a tendency to build up lead and gunk a bit more than other brands. Winchester ammo isn't that bad but a good cleaning in the chamber as suggested above should help.

Experience has convinced me that the M&P 22 Compact likes to be kept clean. I don't question that, I just keep it clean.

The above comments on cleaning and ammo dislikes are consistent with my .22 Compact, which has 10,019 rounds through it.

I would also add that you may need to clean the inside of the mags. The various waxed / coated bullets tend to leave a layer of crud on the inside of the mag at the feed lips. This shows up as poor feeding and failure of the slide to lock back, as the follower gets stuck and doesn't push up evenly. If you have not seen this yet, you probably will with time.