Edit: Got it to unstuck somehow. Original thread in Russian seems to attribute it to constantly clicking on the screen while switching?
Edit2: Spoke too soon. I opened the shop and got back stuck again… 
Edit3: Now it’s working. Good Luck all.
Same issue in other thread says he got unstuck but didn’t work for me:
Any way to restart/reset game in progress? - Technical Support - Hearthstone Forums (blizzard.com)
Source in Russian:
Весит на входе с окном “Переподключение” - Техническая поддержка - Hearthstone Forums (blizzard.com)