I have a Magnitude SV34 with the same Inverter. Based on the E10 it does sound like an issue with the Inverter.
I would check all of the battery cable connections. It is not unexpected for there to be a loose cable.
Check the positive and negative cables at the Inverter and then check the positive and negative cables at the batteries.
The positive cable at the battery will first connect into a 300A MRBF Terminal Fuse Block. Make sure the cable is tight and the connection to the battery is also tight.
One other thing to check too.....
There is a control panel on the inverter in addition to the remote panel inside the coach. Make sure the power switch on the control panel built into the top of the Inverter is Off (button should be out). If that power button is On, it over-rides the remote panel in the coach.
If none of that checks out, I would contact Thor Warranty Customer Services, tell them about what you have done (including talking to Xantrex support) and ask them to send you a new Inverter. It is not a difficult swap but you do need to be cautious with both the AC and DC power.