If you go to Firmware -> Configure are you on the standard or relaxed firmware? I had some weird issues with my monitor and 960p mode. I just keep it at 1080p as it works perfect every time, 960p mode my monitor would have a similar issue to yours but it sounds like you have tested at 1080p as well.
If you are on relaxed I would definitely switch to standard firmware for troubleshooting as it is fully hdmi compliant.
edit: I'm dumb, you said it's set to standard. Not sure what it could be if 1080p is doing it as well