Just in case someone else comes across what happened to me....

I am on Windows 10 and somehow I changed my setting to "not show animations in Windows" in my display settings. I was working on a carousel with slide and fade and finished it. I usually preview in Edge and other browsers....resting assured there was no problems for a simple Bootstrap carousel in Firefox or Chrome. transitions happening when I viewed ...what the heck ? Every other browser but those two ?

So in Booststrap.css is a setting now that if the user turns off Windows "not show animation in Windows" it applies a media query prefers-reduced-motion which turns off transitions on certain components.

There is a setting in the sass files to disable this new feature....but for the sake of vertigo....I will leave it on.

Interesting. I have window up and down animations disable on my Windows 7 machine, but animate controls inside windows is still enabled. My settings have not affected website transitions, so it must only take effect when you disable animations inside system windows (not Windows.)

I would have NEVER in a million years suspected this if I found transitions weren't working. Good catch @Twinstream !

It does make one wonder if I should now notify the user upon loading my site that they have prefers-reduced-motion enabled with a alert pop-up ?