Boy, given what you have done this is somewhat of a mystery, particular for this machine. The way it is designed this is not likely to happen, but that is not much comfort for you.

Check to see if the tub is settling correctly when it goes into the spin mode. The inner tub floats during the was cycle and drops back onto the drive shaft when it drains. It may not be dropping back correctly due to something caught in the tub or for some other reason.

That's about all I got, maybe someone else can chime in with their thoughts.