Blog pagination and/or archives returning 404

Hi,
My website has developed an issue with the pagination, and/or archives depending on setup, which causes 404 errors (not sure when this first developed).

All works fine when my blog url is different to my category base e.g.
blog = ‘cfmblog’ (url = https://mywebsite/cfmblog/page/2/)
category base = ‘blog’ (url = https://mywebsite/blog/articles/environment/)

When I set both to ‘blog’ (which is ideally what I would like to keep) I get 404 errors when navigating to page 2 of the blog. When this occurs the archives work fine.

What I’ve tried….
Switching themes, then back again = page nav works but archives then give a 404.
If I then refresh my permalinks (to any custom set) the pagination will now give 404 while the archives work!
I’ve tried deactivating all plugins, including deleting my wp super cache plugin.

Any thoughts as to what has happened to my WP, and any fix suggestions would be greatly appreciated.

Cheers,

Antony