Answer
This happens because the view actually used by the Customer Order Lines screen doesn't have a default home page connected to it for lobby-link purposes, unlike the plainer CUSTOMER_ORDER_LINE view. Rather than switching the data source's view (which may lose fields the saved search depends on), you can instead give the Lobby Link element a direct page address instead of relying on the view's default home page — for Customer Order Lines specifically, that address is ifsapf:tbwOverviewCustOrdLine. Specifying the address directly bypasses the missing default-home-page association entirely.