The below observations have held true with builds 42 and 50, the only 2 versions I have tried:
I have a similar (or maybe the same...I haven't done enough testing yet) issue. I noticed very frequent and sudden brightness fluctuations in Love In Taipai, a few hundred over the course of the movie, and when I checked with MPC-HC's Info tool it was listed as "SMPTE ST 2094 App 4, Version 1, HDR10+ Profile B compatible". Since I am not technically educated enough to know whether or not it is the fault of the DTM, I have narrowed down the problem only to JRVR in general, as when I switch to Red October madVR the problem goes away. I planned on doing more testing before reporting this problem, but since this thread was already started I thought I would at least confirm that I have noticed the behavior, though I have not examined enough other content to reach any conclusions.
While I am here, I might as well report another problem I have noticed with JRVR:
When the APL is low AND has no bright elements in it, the graininess of the film increases and actually shimmers at times. Once there is a bright element in the frame, then the graininess and shimmering disappear and the picture once again looks solid. This is very noticeable on a 158" scope screen (167" 16:9), where people with smaller screens might not notice the effect. The "shimmering" can also give the appearance of movement or "crawl". This happens on any video, not just HDR10+ or even with HDR (1080p does the same thing), so I suspect the issue is with the VR in general, not the tone mapping. Again, more testing is necessary. And again, switching to MC's stock version of madVR fixes this problem as well.