I get to deal with weird stuff like this at work all the time. Based on the behavior, I'd guess there's a clock and/or data running at a harmonic of the wifi data. Freezing seems to indicate it's coupling into the core of the LCD controller board, which again I would guess is a timing violation or data corruption. Where it's coupling in is a bit hard to determine without further testing. It could be the video cable, could be the power cable (not likely), could be the LCD panel itself acting as an antenna, or an interconnect cable that is poorly shielded or just the right length to couple in wifi. It could also be power supply ripple caused by a feedback loop getting energy coupled in, though if that's possible then there's not enough timing margin to begin with.
I suggest a number of tests to narrow down details of the source:
- Test 2.4GHz and 5GHz independently. Test each wifi channel independently.
- Try a different length cable. Try a different brand cable. Does this monitor remain on with nothing connected? If so then try it with no cable, or no PC at the end.
- Try different antenna angles. Try different TX power levels (at what level does it start).
Based on those results I'd have more recommendations.
If someone wants the real root cause, feel free to send me one and I'll debug it (though it will probably require disassembly).