The "Splice plate" component requires separate member ends for its correct definition. If the member is separated by a node of type 'Standard', these two member ends must not be defined as type 'Continuous' in the add-on on the 'Members' tab, because otherwise the 'Splice plate' component does not detect the second connected member. It is correct to set the type to 'Member end'.
This type of joint cannot be defined at a node of type 'On member' (blue nodes) because the member is not divided or separated by this node type. Thus, the 'Splice plate' component does not detect the second connected member.
Link to:
FAQ 5776 | "Bolted Splice Joint on I-Beam Part 1/2"