I have been dealing with this issue for a few days. I can’t log in to my account while using the app from AppStore on Iphone 8. Every time I try to log in, the game is constantly crashing and I’m back on my desktop. I have reinstalled the game many times already and I also did delete all the data from my device (also those gathered on backup). Also, I have got the latest ios version. I have been playing Hearthstone on ios for about 2,5 years and so far I havent got such a difficulties.
I tried many different ways to fix it by myself but I have stucked. I would appreciate your help with this issue!
Hey igorp11!
If you would like to post your question on our English-speaking Forum, please do so here:
https://eu.forums.blizzard.com/en/hearthstone/ 
And regarding the issue itself - our support capabilities are actually very limited when it comes to mobile devices. We can recommend clearing the app’s data, reinstalling it fully, and finally factory wiping the device to reinstall everything from scratch (loading a mirrored backup can actually still bring back corrupted data, so it is not always recommended). And, if everything fails, the last resort is to contact the technical support team of your phone’s manufacturer.
Best of luck!