It seems like recent problems with Blizzard app (Hearthstone, World of Warcraft, Diablo 3, ...) are caused by old wine mono version - 4.5.6. I was able to modify my local mono.lst file and force PlayOnLinux to use version 4.7.0. It fixes the problem with Blizzard app.
Is it possible to update: http://wine.playonlinux.com/mono/ repository?
I searched GitHub repo for this, but I can't find. So I'm unable to do a pull request.
If we update wine mono versions for wine 2.9 and up, it should fix Blizzard app problems. It worked on my computer.