You know what this reminds me of? Its an issue I've had with Linux for years, that has never been resolved. And I think all more then likely the issue is caused, due to hardware entering sleep mode, basically what FrenchPress said.
However, I can expand upon that. A new law went into effect, that more and more states throughout our country have been adopting in the US. All computers sold from 2018 and on, which also includes monitors BTW, have to meet power consumption standards while idle.
This means, that when your computer is completely idle, and its not being used to do anything, it must consume much less power, then computer's used to, back in the old days. So what is the issue that I have had, that I think is very much related to the issue you are having you ask?
Well, I use an external display, connected via HDMI, to the notebook computer. When the TV stays on, I have 0-issues with signal from the notebook. But, if I leave the computer on, but turn the TV off for several minutes. When I go to turn the TV back on, no signal from the computer.
It forced me to have to restart the computer, in order to get a signal back to the TV, and its a really fricking annoying thing, especially since my Corsair K95 keyboard doesn't properly load in to the OS usually first time, and I have to do another fricking reboot, to get the darn keyboard to fire up with teh computer properly.
Yeah, I know, another issue. But I think these problems stem from the same thing. Its all because of these new power consumption related standards. Hey, I am all for computers consuming less power on our power grid, and going for a more GREEN approach.
But I what I don't like, is having to do unnecessary reboots, just so I can use my computer again, thats total BS. But what other choice do I have? There is no working solution to any of these issues.