React: Cannot read properties of undefined (reading 'split')

Uncaught (in promise) TypeError: Cannot read properties of undefined (reading 'split')
    at index.mjs:968:38
    at DefaultNotification.createRenderEffect.e [as fn] (index.mjs:7880:17)

  const styleFuncMemo = createMemo(
    () => ({
      key,
      className,
      iconKey,
      context
    }) => {
      const appearanceKeyParts = key.split("__");
...