Hello again,
I finally found the problem.
It was a problem with the ruby version. Specifically, it was because the configuraion file for opennebula daemon had also been modified in /lib/systemd/system/opennebula.service to use the ruby version installed using rvm.
This configuration file for the demon should not be modified, only those of the demons such as opennebula-sunstone.service, opennebula-flow.service, etc.
Once the changes in this file were undone everything has returned to work as expected.
Thanks especially to @atodorov_storpool and @cgonzalez.