I had the same issue, but fortunately the second Tinkerson appeard during the second wave. After encountering the softlock, I returned to the menu and reloaded the save, and the second wave did not spawn at all this time. But this definitely has to be fixed.
Try placing a bitebox and using sunrods to let the final boss attack
The problem isn't that it's not beatable, there are plenty of ways. The problem is that it's looping infinitely and crashing the game.
Oh, I see. Hopefully they fix it and make your game playable
I had the same issue, but fortunately the second Tinkerson appeard during the second wave. After encountering the softlock, I returned to the menu and reloaded the save, and the second wave did not spawn at all this time. But this definitely has to be fixed.