edit: Thanks! Resolved. Several posters were right - this has something to do with resolution and screen size. No idea why it is rendering differently the past couple days.

I figured it was a Mobile-view thing.

is vertical, but does appear when it's horizontal.

There's just so much DU can stuff into a small screen, so it adjusts.
Sometimes, putting a phone into landscape mode changes things (IIRC)

plenty of size available on screen. But appreciate help and suggestions.

Remote debugging is the bane of my existence.
Good luck.

edit: Thanks! Resolved. Several posters were right - this has something to do with resolution and screen size. No idea why it is rendering differently the past couple days. Nonetheless - that was what was a the root of it.

That could be getting confused, or sometimes you'll see a URL with a m.site.com, where the m means "The user has a mobile device"

I did a search on "html response" regarding window size, and it's so embedded that a website merely writes javascript code:

var w = window.innerWidth;
var h = window.innerHeight;

Gone are the good old days when the browser response string was a big deal.
As usual, resetting the browser, however that's done often helps. (all I see here is "clear history and data" )
It also erases your history of browsing naughty sites (unless Google is tracking you somehow) I use browser extensions and built-ins to limit or stop tracking cookies. Too complex to discuss here.

HTH!