There was an interview on Laine on YLE website (Finnish national broadcaster), where he talks about his problems in a bit more detail for the first time AFAIK. I know people have moved on, but since it's the first time he has really said anything specific about things, thought some people might still find it of value.
TL;DR - his problems with depression and sleep deprivation started after his father died and seems like the injuries 23-24 were the last straw, so pretty much confirms what I guess most people thought about it.
Some quotes from the interview, translations mine.
"Things started going downhill a few years ago when my father died. After that I started having all sorts of sleep issues, I couldn't get enough sleep and the tiredness added up. On top of that there were the injuries and other things." (edit: not sure what the 'other things' here are, but maybe braking up with his long term girlfriend? I don't remember when that happened)
"The mental problems started to affect everything. It started affecting my work, that is playing hockey. Personal relationships also suffered, I found no joy in anything."
"I had weeks where I didn't want to see anyone or leave home. I didn't want to do anything and I didn't enjoy the things I normally enjoy. I had no energy and nothing interested me."
on 23-24
"Again got injured a couple times right at the start of season and I started getting really depressed. Just as I was about to get back to playing, I just suddenly started feeling like I just can't do this anymore."
"[entering PAP] was one of the most difficult decisions I've had to make for myself, after all hockey is a sport I've loved all my life and which I've given my everything to. Having to put playing hockey to the sidelines was a difficult decision, but the best one I've ever made."