https://bugs.winehq.org/show_bug.cgi?id=29384
--- Comment #85 from testator@protonmail.ch --- Yes strange as it sounds you have that correct. I ran battle.net with a fresh prefix under wine-vanilla-9.6 without any patches and it did the same thing as without staged writecopy or without the userfaultfd writecopy. That is the langauge selection screen appears, after selecting language it hangs forever at "downloading battle.net update 45%" no segfaults.
I had a hunch about something. I compiled wine-staging-9.6 with the userfaultfd patch again but this time with far less aggresive optimization flags, e.g no lto or -O3. It results in battle.net launching in staging-9.6 with userfaultfd to the same thing as vanilla wine, language select followed by stuck at 45% forever. Maybe i'm just an idiot at installing battle.net in a fresh prefix but preinstalled doesn't work either with strange dll import errors. I'm going to take a wild guess here and say since it works for you and kimball its a musl libc thing. There's something to bisect between wine 9.2 and 9.3 since other CEF apps didn't have this issue at that time. I've been sticking to 9.2 hoping upstream would randomly fix it but here we are....
And this is definitely not your bug? Sorry for the confusion and the spam.