When the docker containers had no DNS resolution, the symptom is a failure to validate the license key, but we may get the same symptom due to a real license issue or lack / wrong proxy configuration. Opening the uiserver-services.log reveals the actual problem.
At the moment the workaround for it was editing the docker-compose.yml - under /opt/exabeam/data/sk4 , adding under sk4tomcat, appconnect and healthreport services the org dns (dns: <ip>). The IP for the org DNS server was taken from /etc/resolv.conf
Please note, that during upgrade we replace the docker-compose.yml and the change will be lost.
A better solution would be to configure the docker daemon to use the org DNS.
To do that create or edit the /etc/docker/daemon.json file, adding dns: [<ip>]