My .22lr AR is currently setup with S&W M&P receivers, 16" CMMG barrel, CMMG/Ciener bolt with collar.  

I can't seem to get it to run reliably without a buffer and recoil spring.

Anybody else run into this?  

I don't believe it should require it, I'm guessing it just isn't getting held far enough forward.  

What do you all think?

You need to restrict bolt bounce, either a pressure plug or  buffer spring. Wood dowel will work too

This. The buffer and spring are not needed for the 22 conversion frame and bolt, PROVIDED your upper and lower are in-spec enough to properly secure the frame without them.

Ideally, the frame comes exactly to the back of the upper, and is held in place snugly by the lip of the receiver extension thread ring on the lower, with no room at all to move when the receiver halves are closed. Often that is not the case.

I have a CMMG conversion unit with the locking collar that secures the conversion frame to the barrel extension, and that setup does not require anything in the buffer tube at all to work properly, even if there's a sloppy fit between the upper and lower combination it may be installed in at the time.

I have another (older, Ciener) conversion unit in a dedicated upper/lower combo, that can move back and forth during firing if there's not a significant amount of pressure applied to the conversion frame backplate. That unit gets a buffer, spring, and pressure plug inserted to keep the frame from moving around.

Do you have a 3D Printer ?
There is one on Thingiverse...