You can resolve the machine.secret problem by executing
commit-ox-ucr-variables
followed by:
service open-xchange restart
to write the open-xchange config set by the UCR.
Alternativly you can trigger the password rotation via:
/usr/lib/univention-server/server_password_change.d/univention-ox postchange
This is also going to reload the ox service.
This can be found in our knowledge base article 13747