Hello, I have the same issue with M5Core2. The device worked for a couple of days, but now screen is blank. I've tried the following all without success: (i) erasing flash and reloading the UI-Flow Core2 firmware, (ii) erasing flash and loading the Core2FactoryTest, (iii) erasing flash and loading the M5Core2TouchPanelRecovery, (iii) used "Firmware Exporter" from M5Burner to save the 16MB binary image of a good working M5Core2 and then used ESPTools to burn that image onto the broken M5Core2.

I am curious if you have found a solution to your similar blank screen problem.