Change Assignment quick action missing

Summary:

We are using customised roles. We are starting to ask our staff to move completely away from the classic UI and use the responsive UI more often. One of the issues that we have discovered is that our custom HR role can edit assignments in the classic UI and has access to Employment Info but does not get the action of "Change Assignment". On looking at the documentation for the responsive UI I cannot see any reference to a privilege that would allow access to this and as they are already able to access the classic UI through manage employment