Internet Explorer "Container Busting" Issue

Hello,

I run about 10+ sites, all with GeneratePress & no issues... But today, I tried to migrate another 2 sites over to GeneratePress & I've hit a problem with the footer & header moving to the right-hand side of the page & causing a horizontal scroll on Internet Explorer.

See the image below for an example (problem highlighted in red):

If I center align the footer items via settings it works fine, but the moment I try to align the footer bar to the left or right, instead of aligning properly (as it does on my other sites), the entire footer moves over, causing horizontal scroll.

I disabled all plugins, disabled all caching, disabled the bar shown in the screenshot above, removed all custom CSS & tried it with a default installation of GP... Same thing happened - and it happens if I choose "use navigation as header", too.

What's baffled me the most is the fact that I have other websites using GeneratePress & the exact same settings & it works absolutely fine. I literally cannot figure out why the header/footers of these 2 sites are getting pushed over... I can't see any difference at all between these & my other sites.

I even tried importing a theme from SiteLibrary & was hit with the same issue on that as well.

Any help would be much appreciated as I'm really pulling my hair out over this one, lol.