Okay, I’m going to take a wild stab at this… because I had the issue early on with the Longitude.
Others will correct me if I’m wrong (as forums do), but I seem to remember it had something to do with the aircrafts batteries going dead. I assume you are flying the standard Longitude (no mods, etc…)?
I have both the Alpha and Bravo, but when this issue happened to me, it was early on when I only had the Alpha and was just learning to use the Longitude.
It was something about a main switch (likely the Master or Avionics) on the Alpha causing the aircraft batteries to deplete unrealistically fast, while you were away at the menus (even though your engines are running). I tried to recreate your problem this morning, as I was curious, but couldn’t… I’m flying the Longitude fine, after a trip out to the config menu, with or without making any changes.
I don’t know… perhaps my mentioning it will cause someone to recall this bug.
Then again, I could just be reaching for straws here… but I did have a similar experience… and more than once, if I remember.
Just my $.02
Jim-Sim