this sounds very similar to a behavior what i had.
i discribes it here in the forum and steinberg (crode) has no clue what it can be.
there must be a old tread. ( i dont find it, because of the new forum, i´ve lost my old nickname starcorp)
i had lost a project too, but it was only for testing.
it happens not again to me with 1.6
if you a guy with daw experience you know : strg+s every time
for cubasis it is the snapshot. i´m doing it after every editing or every minute.