Startup stuck updating to 1.3.6?

I've a fresh install on a new pi3, with a new card, connected to an Ender3 (not sure that's relevant, we're not getting that far).
According to the logs, it's trying to upgrade to 1.3.6 and getting hung.
On my other installations, I usually handle the major updates via the UI.
Logs are located here:
Any pointers appreciated.