Three Jack Stands or Four?

that certainly did make me stop and reread your post several times.
thoughts...
are all the jackstands actually the same length?
or are they cheaper chinese stands?
is your floor actually level?

if the answer is yes to those...then..it has to be the car itself....?
if so,then now would be the time to fix that And install subframe connectors,
so it doesnt happen again.