I have no idea what the rings in the beam came from, but you can find out: set the light at a very low mode, look into the light, and slowly adjust the angle of the light so that the rings are directly shining into your eyes. You will see a sudden spike in brightness and just need to identify what part of the light suddenly got brighter--that part would be responsible for creating the rings.
Regarding the dark center spot: I've had the same issue with every 219C and a LH351D, and it wasn't caused by focusing. Some LEDs (especially high CRI ones it seems) have phosphors in which colors aren't evenly distributed, with the outer edges of the phosphor tending magenta and the center tending green. The problem is particularly prominent in a shallow reflector (small height:diameter ratio) like with the S2+; the same LED reflowed into a T2, which has a more elongated reflector, doesn't have the brown spot at all. Scroll down in this thread to see a very bad case of this problem in a Nichia 144A.