Hi
To get rid of the consequence of the fact that subnet belongs to 2 sites please identify which site the subnet should belong to.
Then run the following command in the SQL Studio
delete from ResourceAssociation
where ResourceAssociationTypeGuid = 'F71ABA8C-8823-44c8-A750-F03DE84DC5F6'
and ParentResourceGuid = '<guid of the WRONG site>'
and ChildResourceGuid = '<guid of Subnet>'
Then I would recommend to restart at least w3wp . Ideally AexSVC should be restarted as well.
Regards
Arthur