I don't think this is the only time this has happened to him? He's an absolute legend of the game and it is noteworthy (to me at least) that he hasn't gone off the rails, although Russia's perspective is that he has.
There might have been some lead in the chess pieces in Russia. Fisher was completely mad and played his famous Spassky match. Next came Karpov, who isn't exactly mad but has some pretty horrible takes on global and social issues. Kasparov defected (? Not sure that's the correct term), and then Kramnick is completely mad and a disgrace to the game.
Disclaimer to say I don't really think there is some connection here, but you could maybe make one if you wanted to.

I've always liked how this show seems to concentrate on stories other than the championship, I'll be interested to see what they have in store.