I got this exact issue also, box stays responsive to ssh, etc. systemctl restart doesn’t help. Only “fix” is pull power and use it right away, as long as it doesn’t “go to sleep” the box is fine. once left while I go to bed, etc. Next morning turn on the TV and it’s “no signal” I tried the tests above nothing helped. This has only been since v19 release. I’ve tried reinstalling a fresh image of 19 and still same issue.
Not particularly helpful as I can’t provide logs, but my brother was recently describing the same behaviour on his Vero 4K+…connected directly to his Panasonic oled, sound routed to amp via optical cable, gui set to 1080p and screensaver set to dim. If he doesn’t use his Vero for a few days (or maybe less, I’m not sure) he’s frequently found his machine to be unresponsive with a blank screen, requiring a reboot to get it going again. However, he said this was happening prior to upgrading his Vero to kodi 19, but apparently has happened since. We have identical kodi setups on our Vero 4K+s and I’ve never experienced this, although his Vero will see longer periods of inactivity than mine for sure. Excluding other hardware, the only difference is that I haven’t installed a fresh osmc image on his machine for around 18 months. FYI we’re also using Logitech Harmony remotes (connecting to hub via Bluetooth) as the OP mentioned this.
This happens to me sometimes with my Vero4k+ connected through my Yamaha AVR to my LG OLED TV.
Switching the AVR input to the Cablebox and back to the vero once or twice always brings the video back. I never have to power cycle the Vero.
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I had this yesterday, not for the first time, and had time to try a few things before the TV show I wanted to watch. Vero->Yamaha->Panasonic. Even the Yamaha OSD was not available on the TV. SSH to Vero was working. Switching AVR inputs did not work. Taking the Yamaha out of the chain didn’t work. Re-starting Kodi didn’t work. Only a Vero re-boot followed by power-cycling the Yamaha restored normal service. I don’t use suspend on the Vero and HDMI HPD is not disabled.
This is still periodically happening to me 
I’ve now used keymap to bind the hash key (#) to System->Reboot, and programmed my Harmony remote with a Reboot function by sending # 
a long-press is required (it seems), and it then initiates the reboot of OSMC. Now I just need to see if that works when the unit isn’t displaying anything, as it will be “nicer” than pulling the power on it and easier than having to go to my computer, SSH in, and reboot it remotely 
I had the opportunity to try out my Harmony remote reboot “workaround” yesterday, as all display output was lost again, and it worked like a charm As soon as the unit rebooted, the display was operating fine (from POST onwards).
So I know that network/ssh is still operating, as is Bluetooth. It just seems to be HDMI that shuts down (including audio over HDMI).