We are a repair shop (in business for 17 years. This is the exact same motherboard, same version as what it is replacing. All connections have been checked and re-checked. The link you sent is exactly what I had seen prior to posting my issue, but the HP 23 does not have the factory reset that the monitor in the link has that I'm aware of. It also does not have any vga, dvi, or hdmi connections for attaching an external monitor.
Because of the HP Flat Panel Monitors running the same factory cycling issue, I feel reasonably certain that it is not a problem with the motherboard.
That's quite a good track record you've got, 17yrs is not easy! I respect that.
And I'm glad to make your acquaintance, although, I must clarify, the All-in-one does not have any reset buttons as such, I only posted that to understand that you've been affected by a similar issue as the one described in that article.
Now that it's been confirmed, I recommend you Contact HP as this is a hardware failure and there's nothing we can suggest online to have it fixed, the PC will have to be looked up by the HP certified tech to have it repaired.