Source VMs are deleted after a Failover/Move has been committed even though reverse protection is not chosen as part of the DR operation.
After the failover, the VPG will be in "Needs configuration" state. If the one opens the VPG configuration wizard and does not make any changes by clicking "Done", this would trigger reverse protection on this VPG. The source VM(s) will then be removed from the inventory so that the disk(s) can be attached to the VRA(s) as replication targets/preseed disks.
This is expected behavior.
To avoid, do not edit the VPG post commit unless reverse protection is desired.