This article explains the origin of and solution for the Datto Mac Agent error:
Critical backup failure: CURL Error: https://10.0.000.00:25569/back
Cause and solution
This problem is caused by a conflict between the Datto Mac Agent and Apple FileVault. To have successful backups with the Datto Mac Agent, you must disable Apple FileVault. See this article from Apple: OS X Yosemite: Turn off FileVault encryption.
If you have already performed this step, contact Datto Technical Support for further assistance.