I took my dm900uhd to my friend who have a Samsung 75 "Q67T 4K UHD QLED Smart TV QE75Q67TAU just to see if we have overlooked something
But i can't reproduce your issues.
I tested all HDMI ports direct and also through the Philips soundbar the only way i could get the same issue was if i put the HDMI cable into the wrong port of the dm900uhd
It has 2 port one for "in" and one for "out" where "out" is the correct port.
There are some settings for how the HDMI port is handling 4K / UHD on the TV so tested different settings to see if there was an issue there but everything worked just fine.
And i must say that the picture quality was stunning good for this old box.
I also tested with some very old HDMI cables and still no issue. What i forgot to test but don't see that it should have an impact was, the hdr settings in my dm900uhd
I would maybe suspect either you have the cable in the wrong port on your dm900uhd or your TV has a faulty software / hardware.
All test is done with Factory image and HDMI-CEC off Video settings 2160p 60hz and 1080p 60hz