This problem is fairly new, even though I've been using this monitor as well as other similar ones with my laptop.
What's supposed to happen is that when I wake my laptop from sleep mode, the built in screen should turn on but stay completely black, while the monitor (set as my main screen) should show the box for me to enter my password.

However, if it has been left for a couple hours there seems to be a high chance that the screens will take longer to turn on, and then the monitor will flash grey then black, again and again before finally looking the way it should. Once I've typed my password it will take longer than expected to start back up. During this time I will hear the system sound that indicates something has been plugged into the laptop. The monitor will then disconnect, and after a few seconds of the built in screen turning on and off, it will show my desktop.
There are never any icons on the desktop that it displays, and most worryingly, none of the previously open programs will still be there!
In the display settings, no matter how often I disconnect and connect the monitor, no extra displays can be detected.
I never have anything important that needs to stay open during sleep mode because all actions get put on hold anyway, so I actually find the monitor issues the most annoying, but I'm sure these have arisen because of the odd restarting problem.
Does anyone have any idea what could be causing this?

PS: I noticed that these issues started around about the same time as I started playing Overwatch, but I don't know how that could be related.