I faced this weird behavior inside my sharepoint on-premises 2013.
- finally i have a list item, which i define to have a unique permission, and inside the list item i added the "Network Members" and grant it a Contribute permission as follow:-
But i have noted that the "Network members" group was also removed from the List and the related list items. so i am not sure if this is a bug. as when i add the security group to the sub-site it was not added to the list and list items, since each component have a unique permission. but why when i remove the security group from the sub-site it was removed from the list and list items.. now i can add back the security group to the list and the list items without having to add it first to the sub-site... so can anyone adivce how this is being handled?