Another one of these issues. Some information below.
This is purely a Chrome issue, and solely on my one computer.
No problems on the same computer while viewing in Edge, or in Chrome Incognito. Likewise, on my iPad and phone, there are no problems.
The extra www. started appearing while I was being impatient waiting for the site to 'go live' after updating the hosting and hitting the F5 key.
My Chrome is up to date, checked on whatismybrowser.com
I have followed steps to try and solve this problem using various methods posted, however the problem still persists. As I have said above I can still view the site on other browsers on my computer, so not a great issue. Just wanting to make people aware that this is a thing and see if anyone has stumbled across something that worked.
Edit: After trying a few solutions that didn't appear to help, I went and cleared my browsing data, cache etc. This seems to have resolved the issue.