I feel you have a clutch malfunction with your FAV6800AW machine.
The SM has no test that I can find just the strut removal process starting on page 43 of the SM.
If your FAV6800AW is 3 to 5 yr’s old I would lean toward a Clutch malfunction causing your dc/UC errors in spin cycle.
You can see this post
for the details on the clutch removal process.
For reference with the top raised and the front cover off I over fill the washer with about 6" of water in the tub.
I press down one at a time to both the left front and right front washer tub corners and feel equal resistance to bottom out the struts (about an 1” of travel”) and they spring back to level position equally.
With the tub over filled to the level I mention do you get the same results?
If you do then my next step would be to drop the clutch out as in this post
, clean up and re-lube the roller clutches or replace the clutch if they are rusted up or the clutch spring is broken.
You can turn on the drain pump in service mode page 16 of the SM “Board Output Test - Drain Pump” to empty the tub if you do this test.
Good luck and post back if you have any questions.