Just to confirm that MP's DRR was disabled when I did my madVR testing.Can you try to use MP DRR instead or madVR one (not both) ?
This didn't work; MP's DRR didn't change successfully to 1080p24 when I started a movie. So, I switched off MP's DRR option and re-activated the display modes in madVR.When I get home tonight I'll blank out the display modes in madVR and use MP's DRR instead, and see what happens...
If you can stay on V291, i will try to build a new file for you to test