Hello @alquimista_mx, welcome to the Nextcloud community! 
please check if this How to fix "Encryption App is enabled, but your keys are not initialized." error during login helps.
At the end as far I understand your system is hosted by one company - in such a setup server-side-encryption doesn’t ad any additional security as the company has full access to the server, I would recommend you completely disable encryption and decrypt files to avoid issues.