My guess would be the power supply is putting out something closer to a square wave than a sine wave and the monitor power supply is unable to turn that into DC.
Is there another appliance that I can test to see if that's the issue? I don't have an oscilloscope.
Edit: I just tested powering it from a UPS: It's flickering more now and when it show the correct content it stays for a second more then when powering from the ecoflow.