Yep, me too.Fusion 12 is rock solid for me.
In almost all cases when I've experienced NoF crashing/deleting objects/etc it's due to something I've done. The biggest fault in the beginning was putting objects into NoF from all over my hard drive. Over the years my computer configurations have changed considerably, from number of drives, assignment of drive letters etc. And then there's the times I've moved assets around on my computer.
I learned years ago to ALWAYS copy assets into the NoF site structure before placing them in NoF and that has removed most instability problems for me. It almost always comes down to work flow.