Wow, there have been so many animation glitches.
1) The biggest glitch: the leading Pokemon to appear to be on the other side, yet invisible. This includes move animations, attacking and defending, and the HP bar. This one is usually solved by refreshing the page.
2) Repeated screens (Light Screen / Reflect) animations. Every so often you will see the screens animation repeat.
3) Weird terrain animations. The terrains slide on and off the screen, which is unlike the former fade in fade out animation.
These are only the ones I know, and I've only played on my mono team since this glitch started happening, so it's likely there are more glitches that I don't know. I also know that I'm not the only one experiencing this glitch (there's another person a few posts above).
I have a video of all of these things happening, but couldn't post it because of size. Probably could get around that if necessary, though
View attachment 121339
This is shows a lot of things happening at once. The Tapu Koko is invisible, despite HP bar and "Electric Surge" bar being on the opponents side. You can also see the electric terrain "sliding" onto the screen.
I don't know what happened, honestly. Showdown update maybe?