A community member reports that they upgraded their cluster from DC/OS 1.7.x, to 1.8.9, then from 1.8.9 to 1.9.4. During the latter transition, the migration failed, causing Marathon to come up with no apps or framework id:
It was possible to recover the apps as they were all still stored in Zookeeper, but the root group was completely empty. The frameworkId was not specified, so Marathon registered with a new one; we were able to manually set it back.
We need to investigate to see if I can determine why the upgrade failed.