Help Screen issues upon waking up

[chibae]

My tablet is the 16g Wifi running 5.1.1 It had been rooted by a previous owner but flashed back to stock before I received it about 18 months ago.
In the past couple of months approximately 50% of the time when I "wake it up", either by opening the case cover or pressing the on button the bottom half of the screen stays black for a second or two before it joins the top half of the screen in showing the home screen. Additionally the touch screen it self will become unresponsive for a few seconds.
Thoughts, beyond replacing the tablet?

 

[Octafish]

I have similar issues, mine struggles to wake up, struggles when changing screen orientation, struggles when docking and undocking (official Nexus dock), and struggles with Chrome.

Trying to do a couple of the above together (i.e. picking it up and using it), and it gets so bad that it will reboot.

It is very frustrating that the original buttery smoothness has gone, with no apparent extra load, but patience is key, and once it's going all seems to be fine.

Had mine from new, it's rooted but running stock 5.1.1

Still love it.