For me, the only explanation for empty patterns would be the reload of a previously saved state, with empty patterns, but the arrangement remains. 
Faulty Card ? There would be error messages I guess. There is no function that let you erase several patterns AFAIK.
Projects are auto saved. I’ve never lost a project, even with OT turned off accidentally (and it happened many times with the power socket I fixed) or after a project change. It is safer to save of course. Once saved, CF card .work files are duplicated to .strd files.
I usually don’t save Parts, unless if I want to reload them for live tweaking. They are saved with the project anyway.
Shit happens