Colvale wrote on Feb 27^th, 2019 at 8:55pm:

Something is not quite right somewhere. Just for testing purposes, as I am right now in a 757-300 pax at 36000ft, I selected 10000, hit FL CH, and voila! she is descending as cane be seen by attached

I'll give it another shot -- but these issues stem from the DES NOW button in the FMC and not so much the FL CH (I'll test both though).

I do own the 757-300 but haven't flown it yet. All the issues I've had to date have been with the -200 variant. I almost always have to revert to V/S mode to get the aircraft to descend.

Edit: You cropped out your speed from that screenshot  :'(