Something happened to his health - I have no idea what could that be.

Maybe even just a septum deviation, it completely changes the air flow inside the nose and changes how the vocal chords interact with the air and how it produces sound.

It's even tied to the quality of the air, like getting warm vs. cold air and that dynamic. I'm speculating on this side because I had a surgery and it changed my singing voice a little bit.

My septum deviated again and now I can't sing and getting to breathe between words is way more difficult.