First step would be to isolate the problem. It could be hardware (faulty device) or software (settings conflict between devices). You don't need to necessarily follow this order. Based on your troubleshooting this far, feel free to pick a specific test.
Let's start with software:
Disconnect TV, receiver and player from power for 5 minutes (aka. soft reset). Doesn't resolve?
On the TV, receiver and player copy all your settings and then disable any scaling or video processing (like film/game mode, etc. TV's Color and brightness settings don't need to be changed). Have the TV and player send native signal and receiver simply switch video inputs. Doesn't resolve?
Time to look at hardware:
If possible, switch to a different input on the TV. If the flickering stops, it could be the TV.
Does this happen on any other video sources routed through the Denon? Does it happen if the player is connected to a different receive input? Does it happen when you have the Denon setup menus or Networking input selected? If yes, most likely the Denon is at fault.
Plug the Sony player directly into the cable that you use in Denon HDMI out. If the flickering continues the Denon can be excluded.
Last but not the least, the HDMI cable itself could be faulty. If all the above don't result in isolating the problem, try a different cable.