I think this is pretty well known, but that’s not exactly true. The OSSC can sometimes sync with a board (green light) but your display doesn’t like the signal and you get no picture.
My older Panasonic plasma would suffer from this exact scenario with the OSSC and this PCB. The light on the OSSC would be green but the plasma would just have a black screen. The plasma would not go into the no signal mode, the screen would just stay black. Sometimes setting the output mode to custom and adjusting the settings manually will fix the issue, with certain PCBs. No amount of adjustment could get this PCB to sync with the plasma, but the OSSC never had an issue syncing with it. I confirmed there was no issue with OSSC syncing by running the OSSC HDMI output to a composite/svideo converter and image displayed fine on my CRT. My LG OLED does not have any problem with this PCB on the OSSC and works in the Generic mode.
The 5x can’t even sync with the PCB and has no way to manually adjust the sync settings. I believe the message is “check signal”.
If I change the input mode on 5x to composite it displays a black and white image of the PCB output with garbage at the bottom of the screen. I assume this is the sync information. I believe it also displays that the signal is 50hz.
There issue is the 5x cannot sync with them PCB.