Okay. First, to set the stage:
This occurred while playing the 207th Tavern Brawl Spectacular on PC. I was a Paladin, my opponent was a Mage. We had both chosen the ‘Tol Barad’ ruleset (grants a free spell of same cost as minion played).
The board state was this: opponent had a Splitting Image secret active (which had been created by a Shifting Scroll). We each had several minions on board, but the two that matter for this story are my attacking minion (a 5/5 Silver Hand Recruit - buffed via Sunkeeper Tarim and Quartermaster) and the target (a 3/3 Necromechanic (made a 3/3 by Sunkeeper Tarim).
After I initiated the attack, the secret triggers - spawning a 3/3 copy of the Necromechanic as expected. Once the secret resolved, however, my attacking minion became stuck in mid-air and the attack didn’t finish.
After the freeze happened, I still had minions that could attack and mana to spend. I tried casting a spell to summon a minion - the existing minions on the board shifted over, but no minion appeared. I also tried attacking with my other minions - the green outline went away as if their attack had been spent, but nothing happened.
The rope burned down like normal even after I had pressed end turn, and my hero continued to say his thinking speech (‘Hmmm…,’ ‘I wonder…,’ etc.) long after my turn should have ended. I tried pressing the concede button, but nothing happened. I was forced to alt-F4 out.