0% -> Unmatched selector: %

This is happening in an angular12 project, which is using critters under the hood I assume.

1 rules skipped due to selector errors:
  0% -> Unmatched selector: %

In my styles.scss file I have:

  @keyframes bounce {
    from {
      opacity: 0.10;
      transform: scale(0.9);
    }

    to {
      opacity: 1;
      transform: scale(1);
    }
  }

If I remove this code, the warning disappears.

Probably the scss compiler is turning the from into a 0%, this is just a guess.