Looks like Disney finally fixed its app - have not used D+ in months as I purchased an NVIDIA Shield Pro and now stream everything from that (including Movies Anywhere, CBS All Access, HBO Max and Peacock).
Just for fun loaded the D+ app on my LG, saw a 9/14 update and applied it, and lo and behold the D+ 4K movies now show 4K available and play in 4K.
Still better with the NVIDIA since I can get ATMOS sound in addition to Dolby Vision (the 2016 models do not have eARC and can only output 5.1 max via HDMI).