Sim now seems incapable of rendering overcast consistently or accurately using live weather

Do you have the same issue if you follow the OP’s steps to reproduce it?

No

Provide extra information to complete the original description of the issue:

Checking EGUL again this morning, as I did yesterday morning at about the same time. Today it’s almost perfect again. Visibility to the horizon in all directions, and a solid blanket of cloud cover.

If relevant, provide additional screenshots/video:

EGUL