I had inverter issues that turned out to be a bad ground. It started with my old Magnum inverter after I pulled the battery tray all the way out to fill the batteries. I suspected a loose wire and told my local RV shop (Fat Chance RV and Taco Stand) that I thought it was a loose wire or bad ground. They called and said the inverter was gone (2 years old). They installed a new Xantrex and still had no power. Then they installed a third inverter and with still no power, finally troubleshot the wiring and found.... wait for it..... a bad ground.
I sent the Magnum back to the factory and they refurbed it at no charge. I have a spare.