I'm sorry if you've already checked this, but I had a similar problem with a Windows laptop recently that just would NOT stay in standby. It wasn't a question of if, but how long.
Eventually I found that some "Wake on IP' settings were set to "Wake on any/all IP traffic". I switched those off and now the thing stays in standby/screen blanked.
He sure loves to evangelise "cloning", a.k.a. "copying other people's work". One wonders how anything new or even slightly tailored for each situation will creep into this ecosystem.
To make an analogy, there's usually nothing terribly wrong with the mass-produced clothes that big box stores sell. But it rarely fits that well, looks too stylish, or does much more than cover your nakedness. Often, that's acceptable. But sometimes you need special gear or want a really good quality, tailored shirt.
People still make a living as tailors. In fact, a lot of their work these days is making small alterations to the mass-produced stuff for individual clients.