Then my guess is that there is a device driver which is hanging on boot and preventing things from working.

That device driver might be related to the update or it might not. It may be an existing/old device driver which is suddenly incompatible with windows 10 after the update. The device driver might not be a device driver at all, but rather a kind of malware that disguises itself as a device driver.

In any case, one big difference between safe boot and normal boot is that it doesn't load most of the device drivers during safe boot. I'll bet that's somehow related.