You seem to have overlooked the support template. Can you post the entire stack trace / raw log entry?
That error message is generated by the Encryption app itself, so at a minimum that app is enabled in your environment for some reason (it’s not enabled by default).
when I try to download, to sync or to view some files I have added in the past months.
Does it happen if you create a brand new test file today? I ask because it’s possible that encryption was enabled previously - but is not now. Unless decrypt-all was used, there would be encrypted files left around from that time period.