Setting external display as primary stops external display from receiving signal

I have a PPP with tow-boot installed to SPI. Mobian is running from the SD-card. I have the Pine dock from a OG PP convergence bundle.

The dock is connected to HDMI, a mouse, a keyboard, and a power source. I have booted the PPP by connecting the dock, then holding volume-down to boot from SD-card.

I then open the settings app, navigate to Displays, and then choose the external monitor from the list and press apply. The monitor immediately blanks and receives no further signal. The phone screen shows as would be expected if it was set to the non-primary display and still appears as though connected to the monitor.

Once that happens, I have not found it possible to get HDMI/DP output to work again until rebooting the device. Although, surprisingly, the Mobian logo appears on the external monitor when shutting down the device.

There are also some other random blanking of the monitor, or USB connected devices disappearing, however, the issue described above is the only one I can reliably reproduce.