I am newbie in using UCS and so I am making my experiences by trial and error the last three weeks.
One day I had the problem, that I couldn’t login into nextcloud and could not call any item in Univention management anymore. After increasing the virtual RAM (hint in annother thread of this forum) of my UCS-VM by 1GB everything worked fine again. - The more Univention Apps or packages you install the more memory seem to be needed.
So I guess, that the never ending enable-process may be the result of too less memory which may result to loss of connection to the server services. - If possible, try by increasing the memory of the VM by 512 MB and try again.
Maybe you can find a hint in the logs: