Error while applying public folder permissions

1. Reset Permission Inheritance (for subfolder permission exception) 
Open Exchange Administration Center (EAC) 
Navigate to Public Folders > Select the folder in question 
Check the box “Inherit Parent Folder Permissions” 
Click Save 
2. Re-add User Permissions (for Permission Loss) 
Select the target Public Folder in the EAC
Click “Permissions” tab 
Click “+” to add users/groups 
Select the permission level (e.g. “Editor”) 
Click Save 
3. Clean up invalid permissions (Applicable if the deleted users are still shown) Go to Public Folders in EAC 
Select target folder > click “Permissions” 
Manually delete unknown users/groups (e.g. departed employees) 
Save Changes 
4. Enterprise Solution 
 Bulk Check Permissions: 
Export all public folder permissions in Exchange Management Center (supports CSV export) 
Filter and delete invalid permissions Permissions 
Notes on migrating to Microsoft 365: 
Make sure “Remote Public Folders” mode is enabled 
Permission synchronization may take up to 2 hours