posttrans fail when upgrading gitlab-ce rpm from GitLab 13.4.7-ce.0.el7

Am on RHEL7, using the gitlab-ce rpm.

I have tried upgrading to several different versions but posttrans on the package always fails during gitlab-ctl reconfigure, giving few details apart from "no implicit conversion of nil into String", and the web interface is then left giving a 502.

Running gitlab-ctl reconfigure afterwards gives no error and seemingly fixes the issue, although I may need to reboot, but the problem is not completely gone, at least not at 13.5.7, since I get it again if I then update that to 13.6.5.

Regardless of whether I went through 13.5.7 first, once 13.6.5 is successfully reconfigured I can upgrade to 13.7.4 without error. But although this now appears to work, I am concerned of hidden faults since the underlying reason remains unclear. Also it looked like it may be back with 13.8.0.

Attaching the output when upgrading to 13.5.7, when running reconfigure manually, and chef-stacktrace.out.

chef-stacktrace.out update-13.5.7-output.txt reconfigure-13.5.7.txt