This was happening on my new 12.9” iPad Pro and I read on here to change in Settings>General>Accessibility>Display Accommodations>Auto Brightness (turn off). Since doing that a few months ago, no problems with waking my iPP.I just joined to say that I have experienced something like this with my 10.5". It's happened maybe four or five times in the few months that I've had it, that I will try to wake it and it will stay dark. Nothing rouses it but a hard reset with home+power. I think it was happening before I bought a smart cover. I thought it was an iOS 11 beta issue, but it kept happening after the public release. The last time was a few days ago. Not a huge problem, just peculiar.
Done this , but still happening on iPad Pro 12.9 2017 edition.it happened 6 to 7 times since 2 months I bought it and always happen in landscape mode .This was happening on my new 12.9” iPad Pro and I read on here to change in Settings>General>Accessibility>Display Accommodations>Auto Brightness (turn off). Since doing that a few months ago, no problems with waking my iPP.
Since 2017 it seems you need to upgrade to the latest ios
Here everything is fine for months