I have found the cause of our misery! Apparently by updating our system, a new version of Docker (20.10.6) is installed. I found out (hooray for google) that this version has a problem with disabled IPv6: it ignores this and tries to bind ports using IPv6, even if IPv6 has been disabled on the system. This causes all the errors.
The only solutions are: enabling IPv6 or downgrading Docker. Because IPv6 on Rockstor is disabled intentionally, I chose to downgrade Docker and this worked! all my Rock-ons are functioning now.
In system shell, I entered: sudo zypper install --oldpackage docker-19.03.15_ce-lp152.2.9.1.x86_64
this installs the previous version available in Leap 15.2.