Check the path, then the EDID.
A repeater in the middle of the run
The manual describes the DR HDMI 8K as an HDMI repeater that amplifies and recovers the signal, with equalization (HDMI Equalevel) on both input and output. Placed mid-run, it can often take the place of a separate HDMI amplifier, and it has been used with 50 ft and longer copper, active and fiber cables.
Booster figures from the manual:
Limits worth knowing
No repeater can make a cable carry more bandwidth than it was built for. For 48Gbps links the manual calls for 1500MHz certified or tested cable in copper or fiber. Active and fiber cables also need the power and installation direction their maker specifies.
Tip: if 4K60 or 1080p is stable but a higher-bandwidth format is not, inspect every cable and connection in the link before suspecting the EDID.
Test in this order
- Confirm the source, display or AVR, and each cable are rated for the target format.
- Begin with a lower-bandwidth mode that is known to work.
- Read or copy the sink EDID.
- Offer the source a predefined or modified EDID.
- Raise bandwidth or add one feature at a time, restarting the source after each change.
Changing one thing per step means every result tells you something, instead of several changes masking each other.