I "flew" this recently, and had some issues with the train segment actually being recognised as used (ZFV-EWR-LAS-SFO).

First off I couldn't use the Quik-Trak machines because they need a credit card (which I couldn't do, since the tickets were paid for using Paypal - long story there to do with foreign banks...). Luckily I could collect it with my name+ID at the ticket counter.

On getting to EWR, the machines didn't want to accept my checked luggage, telling my itinerary started in ZFV, and proceeding to printing boarding passes (including the "This is not a boarding pass" for the Amtrak segment). One of the agents seemed to override the system and checked my bag. I also didn't get any SDC options at the kiosk, or on the App, and couldn't get boarding passes on the app at any point during the trip.

My LAS-SFO segment was upgraded while I was on the EWR-LAS segment, but the kiosks at LAS wouldn't let me get a new boarding pass, and also no seat selection was possible either (the GA at the main podium told me I didn't need a new BP, meaning my BP then got flagged when actually boarding - that GA then wrote my new seat by hand onto the BP).

2 days later my EWR-LAS + LAS-SFO segments posted, but no sign of the ZFV-EWR (I have all the boarding passes + amtrak ticket saved, so can send them in in a few days...).

Overall rather annoying because of the IT issues, other than that I liked the connection.