This issue is registered as DEFECT000633740. It is fixed in versions NOS 7.1.0a, 7.2.0, and later versions.
NOS 7.2.0 contains multiple fixes relating to Port Channel Redundancy Group functionality: DEFECT000633740, DEFECT000636021, DEFECT000634220, and DEFECT000634222. Publicized details on each are available in the NOS 7.2.0 release notes. There are no plans to port these fixes to additional earlier releases. Any customer considering using PRG should be running NOS 7.2.0 or later.
In software without the fix for DEFECT000633740, after the DEFECT000633740 issue has occurred, it is possible to recover by entering the config of the affected port-channel-redundancy-group, applying "no activate", and then applying "activate". Executing "no activate" then "activate" under the PRG config forces re-application of PRG behavior to port channels that had failed to apply PRG behavior when receiving their config from the VCS principal.
A reliable method of preventing this issue from happening in all circumstances does not exist. When "vcs replace" is planned it may be possible to avoid the issue by leaving non-ISL interfaces disconnected before running "vcs replace", applying "no activate" and "activate" to the PRG after "vcs replace" is complete, and then connecting non-ISL interfaces as a final step. There is no method of preventing the DEFECT000633740 issue from happening in unplanned situations such as a VDX losing power, losing its config, and receiving its config from the VCS principal. When PRG is configured, upgrading to NOS 7.2.0 or later is higher priority than attempting preventative measures.