Internet pages won't load or are distorted

Macbook Air early 2014 / iOS 10.11.6

Every now again (2-3 times per month) my Macbook will start to play up. It will stop loading websites on the first go and will take me multiple refreshes to get them to load. Once they do load, they will be distorted (images will be layered on top of each other with distorted colours).

It's not a problem with my internet connection. I know this because Spotify continues to run and if I switch to my iPhone's hot spot the problems loading pages will still continue. It occurs on Chrome, Firefox and Safari. It occurs if I delete all my extensions. It occurs if I uninstall and then reinstall Chrome and Firefox.

In the past, I have got it to stop by restarting my computer or by reinstalling iOS. However, it starts happening several days or weeks. I've attached some screenshots of what happens - typically a failure to load the pages until after several refreshes when a distorted version of the website will load.

later.