I don't get why you guys think there needs to be some serious underlying medical condition to explain his vocal issues. If he did have some serious medical condition there's no way he'd even go out on tour. He has four kids, he has a wife, he has a family he clearly loves - there's no way he'd be risking his health like that. (Other than his vocal issues he also seems to be in perfectly good shape.)

He spent three decades of his career abusing his vocal cords pretty heavily and getting away with it, but eventually stuff like that just catches up with you. Add natural aging processes and a bunch of psychological stressors to that and it's really no surprise his voice deteriorated like it did.

People often underestimate the impact a person's mental health can have on their physical health. Jon has said that the entire situation with Richie leaving the band was traumatic for him and he's also said that he used to be bulletproof, but then suddenly he just wasn't anymore. It makes perfect sense that something like that would just make those physical degeneration processes even worse - and also harder to manage.

If you have something that used to come very easily and naturally to you your whole life, but then it suddenly doesn't anymore, you're most likely gonna feel insecure and frustrated and overwhelmed and it won't be easy for you to adjust to that.

He seems so "off" on stage because he's clearly still struggling to adjust. His tendency to slur words together (which is something he's been doing since the 2000s) probably got worse because he feels like it makes it easier to hit the right notes. His timing is off because he takes too long to prepare the notes he's gonna sing and get his voice under control. His tone gets weird because he's probably afraid of singing some atrociously wrong note or his voice cracking, so he tries to keep his voice "small" (which is probably also why he still sounds more like himself on higher notes, because you can't be shy about a high note - either you really go for it or there won't be any note coming out at all). He spent a lot of the last tour just standing glued to the microphone, now he's moving around more again, but it sometimes seems awkward because it doesn't come that naturally to him anymore and he's most likely still preoccupied with his voice.

It's a shame it has come to this point and I feel really bad for him because losing your instrument like that must really be awful, but I don't think it's anything more serious than that.