Hello @Seroga88i and welcome.
I’d like to ask you about your setup if you don’t mind.
It was probably because of low entropy. You could try haveged, although some says that faking randomness it’s a trick that could compromise security of the generated keys.
Another thing you can try is generate random events on your server (e.g. do a find / to read all of your filesystem tree, generate random content in files, anything I/O related should do to help generating entropy).
Nevertheless, it should be a matter a time, sometimes a long time, but the wait will eventually end. It’s not strictly a matter of computing power.
Did you change the Dockerfile to use Ubuntu or are you talking about the host system here?