"System issue" dialogue, after booting without HDMI

[lolliffe]

I have a replicable issue with video/system. Install Ubu-20.04, Desktopify it with MATE. Everything is awesome. Install x11vnc, and it works beautifully. If I shut down, unplug the HDMI, boot back up, the VNC now rejects the connection. I ssh over, and shut it down gracefully. Plug the HDMI back in, boot up, and now have a screen flicker, and a dialogue box ("Cancel" or "Report Issue") about a non-specific (no code, or comment) system issue, that will continue to intermittently pop back up, but I'm generally back in business. I've done this four times, with the exact same outcome. I'd like to be able to boot into MATE without HDMI, and connect to the headless Pi via VNC.

Sorry I didn't screen shot the error. Let me know what other info would be helpful. Pi4-2Gb, out-of-the-box, no overclock, Samsung Pro Endurance 32Gb SD