The example https://cldup.com/3gYZzqJk0K.html regressed in r260360, it uses an animation-wide timing function with a y value outside of the [0-1] range.
This is a specific case of bug 215918 that we should be able to address.
Created attachment 427661 [details]
Created attachment 427677 [details]
Patch for landing
Committed r276966 (237296@main): <https://commits.webkit.org/237296@main>
All reviewed patches have been landed. Closing bug and clearing flags on attachment 427677 [details].