On the latest beta, I had an issue with an image that dims on hover. The image would sometimes remain stuck in the dimmed state, with further mouse hovers doing nothing.

I was able to reliably reproduce the problem by very quickly moving the mouse across the picture several times.

The JS of Semantic UI bugs out at line 16972:

return module.cache.animation || false;

The message:

Uncaught TypeError: Cannot read property 'animation' of undefined

I didn't dig into the code, but adding the following to the currentAnimation function seems to solve the issue:

if (module.cache === undefined) {
    return false
}