I think by now it's pretty safe to say the following:
They all didn't just forget how to play hockey.
AV didn't forget how to coach - his system worked last year, it's shown glimpses of working this year.
The kids had skills 12 months ago, they still have skills now. They didn't just misplace their 'skills'.
This is not Chuck's fault. Yes it would have been nice to get a Dman for Ivan but there wasn't much available at the time. Hindsight, I wish he pulled the trigger on a trade if it was possible.
So what's left for possible reasons for this sh!tshow?:
There is some kind of feud between players: Vets vs Kids, Hayes gave someone a bad nickname now they hate him...who knows
Coaches lost the room: Maybe they are all tired from so many games, with AV's up-tempo style they just can't keep up and they all need naps. Thus resulting in over-tired kids complaining about their parents coaches.
Rift between the coaches causing factions: Hey it's possible. All 3 were/are NHL head coaches and I bet all think they know how to fix what's happening. Some players buy in to each coach and Lord of the Flies ensues.
The players are just tired from this grueling schedule: This is completely possible. I know my wife is tired of me saying "sorry, Flyers are on" the past 1.5 months. She asked if they are on every day now. So maybe, just maybe the players just have nothing left in the tank. No preseason, maybe little training, COVID break....all that leads to crappy play due to fatigue. Then that fatigue leads to sh!tty play and fissures in the room.
The team as assembled isn't as good as they showed last year: It's entirely possible that this team as assembled is a playoff bubble team. Aging vets, young kids still learning and are still getting used to the NHL gruel, crappy goaltending.... It's a combination that is entirely possible. Not to say that two or three key pieces could be added/removed, the goaltending recovers to average or better and this team is fighting for the division lead.
Am I missing any?
My ranking in order of possibility is 4, 5, 1, 2, 3.