Ah, of course; my mistake.
If it does hang again, you can generate a crash dump of the process at that moment in time using Task Manager.
Manually generated dumps in Crash dumps for bug reports explains how.
It could well be a Windows update as some instability we were seeing with shell extensions that have not changed in a long time went away mysteriously, and until then it was looking like something in the way Windows 10 initializes DLLs (in parallel, which is faster but a lot more complex) may have changed.