The Forum stopped working Sat Aug 20 about 19:30 CDT (-5UTC) after upgrading the Discourse version.
The upgrade was flagged in the admin panel as a problem to be fixed. Clicking the 'upgrade discourse' button was all that was required.
The error is '502 Gateway nginx', which means that there is an nginx service issue on our VM at DO.
Inspection of VM showed that nginx is not installed on our DO. Installed nginx, etc. No joy.
Submitted trouble ticket to DO at 22:00 CDT.