F21 error code / SUD error / heavy load won’t drain

My Kenmore elite washer has been giving me error codes F35 and F21 every once in a while. I have noticed that the heavier the load, such as towels, blankets, and quilts, the more likely I get get an error code and the washer doesn’t drain. This happens for heavier loads on the bulky bedding and on normal wash cycles and when I try to drain and spin. Today I had 5 normal sized towels and all day long I kept getting f21 and SUD errors. Tried clearing the error and even unplugged the machine and left it sit for a while. I could drain and spin with nothing in the washer, but not with the towels in there. This morning I cleaned out the bottom filter and tonight I cleaned out all of the hoses and removed gunk from the hose/gasket that holds the ball and is attached to the pump. The load of towels would spin but not drain. Removed the towels and the washer drained. Added a pair of yoga pants and ran a quick wash cycle and it washed and drained. Any suggestions on what could be wrong with my washer?