Upgrade to 13 stops with "Submitting data to servers...ERRORS"

I just tried to upgrade my Debian (32bit) based Freebpx 12 + Asterisk 13 to Freepbx 13. Downloaded the upgrade tool, started the upgrade process (all checks passed). Completed Steps 1 and 2. When Step 3 starts I get
Submitting data to servers…ERRORS
That’s it. Where to start troubleshooting it?

I’m wondering whether the original poster was able to resolve this problem. I am stuck at the same point in the process with the same error message.

Upgrade using the command line worked. It’s described in wiki. However, I really hated the look of Fpbx 13 so went back to 12 (at least for now while it’s still being supported).

Care to explain?