How to remove RoleAssignments from SPListItem/SPFolder correctly in SharePoint

Question

In the library, I have ParentFolder which contains SubFolder. I have broken role inheritance in both ParentFolder and SubFolder (via a web interface).

But when I remove role assignment for the user in ParentFolder with PowerShell script it disappears in Subfolder too. I don't understand why it disappears if I have broken role inheritance. And how to prevent it? How could I delete role assignment for the user in ParentFolder, but save it in a subfolder?

Here is the code:

$web.AllowUnsafeUpdates = $true
$object.RoleAssignments.Remove($user)
$web.AllowUnsafeUpdates = $true
$object.SystemUpdate($true)

I have SharePoint 2016

Answer 1

This is expected behavior for SharePoint. If User A is in Group 1, and you break inheritance on the folder and sub folder, then remove User A from Group 1 at the Folder level, it will also remove User A from Group 1 at the sub folder level. The way around this is the break inheritance then create a new group at the sub folder level and then assign the users to the new group.