why does my wifi keep disconnecting after wake

Hey,

I recently upgraded my iMac to high sierra and it has caused problems.

1. The computer randomly wakes from sleep and shows the desktop in a

weird blue colour. I have attached the normal and blue colours for

comparison.

2. When it wakes, it drops the internet connection on wifi, and I need to turn the wi-fi off and back on, then it's fine.

Can anyone please help? It's driving me mad. Thanks