He has taken some (all I'll say is) differing views on various foreign policy matters, sound is probably pushing it considering he has been consistently contrarian without any evidence (and after more evidence has to light [1]) and consistently wrong.
[1] Most obvious would probably be his spat with Bellingcat over the identities of the Skripal poisoners. Other examples include pontificating about the DNC emails
https://www.theguardian.com/world/2004/oct/22/politics.forei...
That's a rather dishonest point to make, because no one ever mentions in their CV why/how they left a position.
Furthermore, if you had actually read your own wikipedia article, you'd have know that he was forced to leave after he refused to be quiet on the government supporting a regime that tortured people and hushed that and extraordinary rendition up in order to appease their American buddies.
He seems to be sound.