Weird Issue with Themer

I have a weird issue -
2 sites running on a multisite env and I just adjusted the header of one of the sites the other day, and it was fine.

Today, I am trying to adjust the header for the main site but every time I try to edit the header, it reverts to the second site in the WPMU environment (showing only the header and a page not found).

I trying different variations of the URL (thinking I could bring up the correct site), I have cleared BB Cache on both sites in the WPMU, and cleared cache on SiteGround Supercacher, memcache, etc.

It’s somewhat urgent because I need to remove a “closed for renovation” we placed in the header of the main site in question.

I can still access the second site’s header with no problem -

I have a ticket in but thought I might have some luck here or in FB group.

Any thoughts?