Nextcloud Box rPi3 stuck during initial boot

I, possibly foolishly, decided to upgrade my Nextcloud box to an rPi 3 writing off all the data I had on the old installation.
I have a screen plugged in and a continually scrolling message:
[ ** ] A start job is running for Run devmode firstboot setup (1h 21min 25s / no limit) Nextcloud is initialising.

The documentation suggested 8-9m. How long should I leave it before I give up?

If there is a problem, how can I work out what it is?

Thanks for your help.