Your user permissions based on the AD Synchronization is the high level when compared to changed one
That's why the role is getting changed. Check the AD group role he/she belongs to if the role of the group is higher when compared to the changed role then automatically your selection will be reverted.
Maintain the same level of role-based overall server and sites.
Hope this helps.
Plz mark this answer as correct and helpful to close the thread.
Thanks for your reply. The access that I am referring to is Site Membership. And the role across is common as per the "Minimum Site Role".
I have updated my original query to be more specific and detailed.
Hope this helps in explaining the issue I am facing.