I'm trying to boot into a macOS Sierra installer that I made today. For the last about 20% of the progress bar, it was booting extremely slowly. Now, the progress bar has been stuck for the last ~20 min at what appears to be 100% This happened yesterday and the day before that too. I've tried restarting into this thumb drive multiple times, and it always get stuck here.
Mid-2012 MacBook Pro
Update: this seems to happen when trying to boot to any external device