Weird colour saturation issue happening in Illustrator

I'd love some help with an issue I'm having with Illustrator. I've tried to explain as clearly as possible.

Colours are appearing oversaturated compared to the true colour. I have two separate documents open, with the exact same yellow block of colour and each look different. If I copy the true colour block and paste into the other document, you can see the difference in colour. If I drag the true colour block across the screen, it will change to oversaturated. As I've tested it out in different ways, sometimes the incorrect colour will revert back to normal.

I've attached screenshots.

I should add that I'm similar problems in After Effects. I've exported jpg and png files into AE and they are showing up way oversaturated, despite being true colour in AI.

I've recently migrated to a new Macbook and am using brand new updates of the Adobe CC suite.

Thanks.