Between Milan and Lugano i would use the reservation free regionaltrains just 20mins longer and you save 11€ :)

Thank you, that’s a great tip! I’m still confused about seat reservations in Italy. The Interrail app is telling me I need a seat reservation on certain trains (Bologna to Milano, and Bologna to Venice). However, the DB website is saying no reservations required. Is this because seat reservations are required for Interrail pass holders?

@middleagedbackpacker DB say it not directly but it writes Global Price train which are only trains with compulsory reservation. 

The reservation depends on the train category and not the route. 

In Italy you need a reservation on all high speed trains like Frecciarossa, Frecciargento, Frecciabianca, Eurocity of Trenitalia within Italy (10€/seat each train) and Intercity 3€. For Eurocity of DB-ÖBB-Trenord only optional reservation but you need to pay a fee. 

Regionale (R) and Regionale Veloce RV or Regionale Express (RE) do not need a reservation, it is not possible. Add the trip to the pass and hop on the train.

So this effectively means on the very same route SOME trains MUST RES (frecce=arrow=hi-speed and IC) and others slower, regional not.

This was a very well known trick many yrs among about all passholders-but with these planners all knowledge seems to have dwindled down the drains

Well, not necessarily. In Portugal, you will see this "Global price” for almost every train, including reservation-free regional trains. IMO Trenitalia are sending timetables with missing train attributes; their timetables are incomplete.