Happened to everyone. They are in the phase 2 for rolling out Workspace.AnimationWeightedBlendFix. They made its default behavior “Enabled” instead of disabled, which now applies the new changes to the animation engine to all existing places. You can set it to disabled but the property will be hidden and will be forced to Enabled in future.
If you wanna fix the animations, good luck, especially if you have a lot of them. Here’s their post:
If you scroll to the end you’ll see other people complaining for this update.