I was on the review/Tools tabs today, and across all the sites where I'm 10k (or 2k as appropriate) they started out ok and then became surreal, with the black notification bar repeating further down the page.
I promptly tried another browser (FF) and though it started out ok, after a while it started happening there too.
It's also happening on the site-picking dropdown, and I use that constantly (unlike /tools) so this must be a recent change.
F12 in FF gives me:
Use of getPreventDefault() is deprecated. Use defaultPrevented instead. jquery.min.js:3 TypeError: el.closest(...).find(...).addSpinner is not a function jquery.min.js line 2 > eval:73 TypeError: el.closest(...).find(...).addSpinner is not a function tools:165 TypeError: StackExchange.realtime is undefined full.en.js:1
and now trying it in Chrome has led me to "There are an unusual number of requests coming from this IP address" and that browser can't use any sites (though this one can... which is strange.)
It is definitely related to that spinner. Some . . . animation is supposed to appear while the sections are loading. The page looks ok at first, then the entire page appears where the . . . should be.