SUCCESS! After much playing around with my home page, cutting code and reloading the homepage piece by piece, I found it was actually Google’s adverts that aren’t fluid/responsive.
So, GeneratePress and all it’s add-ons are flawless as ever. Sorry to have been a bother, but thank you for the prompt responses. I’ll mark this thread as resolved, and you can remove it if you want.
Keep up the good work Tom!