Issue 1 (minor):
- ISO 639-1 should be written in lowercase
- ISO 3166-1 Alpha 2 should be written in uppercase
Issue 2 (major):
You seem to be using `rel="alternative" which doesn't exist:
Error: Bad value alternative for attribute rel on element link: The string alternative is not a registered keyword.
Change all alternative occurrences to
alternate. I also recommend that you use a proper markup checker rather than screaming frog, such as W3C validator. By doing it'll help you narrow down problems with more explanation, since its obvious that Screaming Frog failed you in this instance.