I have an M&P 15-22 that I continue to have issues with.

I have watched the videos on how to properly load the magazines...and that helped a little.

I have replaced the extractor with an aftermarket extractor...and that helped a little.

Now the only failure I see is basically this:
The new round is loaded into the chamber but the bolt is stuck half way open with the extracted case in the way.  Also note that the trigger is not reset.

So the bolt is traveling back enough to fully extract the round but something goes wrong during ejection.  Also the bolt is back far enough to start feeding the next round.  But the bolt was not far back enough to reset the hammer.  

If this was a std AR I would say it is a buffer weight/spring issue but I am using the stock spring.

Also ammo has been a mix of big name  such as federal auto match or CCI.

I've had one for about ten years now...had an out of battery discharge last year, sent it back to S&W and it was returned with a new bolt.  That was the first on only problem I've had with that rifle and has again been flawless ever since.  I'm assuming your rifle is clean and I see you're using decent ammo. Are you using an aftermarket trigger/hammer?

Mine would eat almost anything from bulk to Winchester Super-X but I have since switched to CCI standard velocity for plinking and 22 matches.  If the rifle still has problems, call S&W.  They should pay the shipping to and from.

All other parts are stock.

I have about 600 rounds through it,  I have never gone a full mag without issues.  Recently I have 3-4 stoppages per mag (25 rounds).  Early on it was every 4 or 5 rounds.

That kind of performance is sub-par for that rifle.  Give 'em a call and tell them about the issue.  I'm sure they'll make it good

Sounds like the ejector is out of adjustment.  

See: 15-22 ejector fix in middle of post

Interesting...I will have to try that.  Unfortunately It will be about a week until I can try this.

Standard or high velocity rounds?  Or both?

I know most if not all have been high velocity, But likely have had some standard velocity mixed in there.  I have used at least 3 different kinds from my stash.