Comment 1 for bug 2038818

Very important part here, is that feature flags must be enabled BEFORE the upgrade. Moreover, some flags are becoming required since 3.12 for example according to the docs:

https://www.rabbitmq.com/feature-flags.html

So I assume it would be appropriate to enable all feature flags after upgrade is completed and backport that down couple of releases.

Of course, as an alternative we can enable flags before the upgrade to ensure that upgrade won't fail as some flag is now required.