Hi,
could you please check if you are affected by this problem? It reminds me of that issue a lot.
I’m not sure if that is fixed in your Katello version already (target versoin in Bugzilla is 3.15, so probably not since that is not released yet). The Problem is that Katello generates Certificates that last for 30 years by default, and since 2020 this kills some python SSL library used in subscription-manager.
The easiest way is to check if the subscriptions for your newly generated products have an end date of greater than 31.12.2049.
Regards