How does and when Zoom release version updates?

When a Polycom unit is provisioned through Zoom and we do a regular Polycom firmware update through the unit admin console it reverts back within 5 minutes.

When this same unit is not provisioned by Zoom the version remains updated to whatever version was selected for updating the unit.

This is due to Zoom somehow preventing certain firmware releases to be deployed and I need to understand how this is managed and why the version is kept at 5.9 by Zoom.

I can't find any related article in KB and Public Article to answer this question.

I hope you can point me in the correct direction. 

Thank you