I recently installed the latest version of Anki. Suddenly, the CSS animations in some of my cards stopped working, e.g. https://ankiweb.net/shared/info/3645353967, which shows a flashing light to represent Morse code.

I did some digging around and discovered that the animation CSS styles used by the card were being overridden by something, so that the style ended up disabled in the final computed CSS. But if I added !important at the end of the style, it would suddenly work again. Super weird.

It turns out that the “Reduce motion” checkbox had been checked in the main settings menu - for some reason Anki didn’t conserve my settings when I updated. Unchecking this option solved the problem.

I hope this helps!