I almost suggested using Serial here, but obviously that’s impossible since those pins are taken by HyperPixel itsef! Yes, this is a tricky one! Sometimes you can see issues by running
dmesg after the system has booted- assuming it’s booted.
Not a simple way, but people have discussed techniques on this forum. Since the config is one of the first things the Pi loads on boot, that involves swapping the config file (using a menu either after, or early in the boot process) and rebooting.
It’s worth trying
hyperpixel-init and seeing if that works. It’s possible it’s not being run at startup.
Not that I’ve seen so far. And I suspect that’s unlikely to be the cause.
Possible, but unlikely. I don’t think there have been any major updates since we launched HyperPixel.
I think your best bet is to SSH in and try
hyperpixel-init, it might be that the scripts to run HyperPixel aren’t being launched on startup.