For me it stops at some point declaring the "download" failed (though it's already done downloading). System logs contain the message "BridgeOS personalization failed."

Update: already gotten two kernel panics the past few days. Investigating at the one from just now, looks like it's caused by a page fault in BridgeOS. EDIT: Ah no, the "Problem report for macOS" looks to be pointing at Firefox? Process name corresponding to current thread: firefox