All of the above. To verify, you are experiencing chainsuck, in other words, as you pedal, the chain doesn't release from the chainring at the bottom and gets pulled back up on the backside? Generally 10 and 11 speed chainrings should work just fine interchangeably, but maybe in your exact case it doesn't. I had issues that my chain wouldn't drop off the big ring when I used a Shimano 10 speed chain on my SRAM 10 speed crankset. The first thing I would check is that there is no damaged tooth on the chainring, and that there is sufficient clearance between the teeth and the spider. Since you are using a Shimano ring on an FSA crank, maybe the shaping of the spider is such that the chain is getting jammed against the spider at certain positions. If that all looks good, swapping in a new chain would be the first try, a stretched chain seems the most likely candidate. Yes, chainrings are made in matching pairs for best shifting, but that obviously only affects shifting from one to another. If we understand you correctly your issue is only related to the small chaining and the chain.
Hi Slim- I agree with you. BTW --- the chain on my bike is virtually new, as are all the components since this is a new bike. I think that changing the cassette from an 11-32 to an 11-36 11 speed will give me no problems. I've already done that on my 11-speed road bike with a medium cage derailleur. Just screwing in the b-screw a few turns and everything works great. Unfortunately, the only 11 speed 11-36 cassette I can find is the $180 IRD.