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%enter image description here enter image description here 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

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