I am running window 10 and recently (this problem may have to do with updates) when my monitor goes to sleep it has a difficult time waking. It takes anywhere from 30 seconds to over a minute to wake up. I have shut it down, messed with disconnecting and reconnecting cables but no results. This has been going on for about 2-3 weeks, so if it is an upgrade from microsoft, how is it possible to do a system recovery and get the right update culprit - if that is really what is going on.
I would advise AGAINST doing a system recovery as those erase everything and require you to restart from scratch -- a high price to pay for monitor problems.
You need to go into Settings, Update & Security --> Windows Update.
Then, choose Advanced Options --> History to see when updates were last applied. If you see any that include device drivers, those could be the problem. So, if you can, you should see if you can rollback the drivers that are causing the problem. You do this by going into Device Manager, seeing if the appropriate device is still listed, and if so, trying to rollback the last driver update.