I don't think ambiguity was the problem with the old version, but this was: "The license granted hereunder will terminate ... for anyone that makes any claim ..

I don't think ambiguity was the problem with the old version, but this was: "The license granted hereunder will terminate ... for anyone that makes any claim ... that any right in any patent claim of Facebook is invalid or unenforceable." That's pretty clear and unambiguous. And many people find it clearly unacceptable. The new version seems... certainly a lot more complicated. It looks to me like it merely prevents you from accusing Facebook of infringing your patents, but no longer prevents you from trying to invalidate their patents if they attack you. But for all I know it could be saying exactly the same thing as the old one in a more obfuscated way.