Maytag Epoc Z MHWZ400TQ01 - F21 intermittent drain problem

[Milly101]

Model: MHWZ400TQ01 - front load clothes washer 

So this machine always worked well, but recently it has been throwing code f21 and code f20. Here is what I have done thus far, but yet still have F21 code. For reference when the code shows up, if I cancel and then do a manual spin cycle the machine drains fine. 

1. Removed all the hoses from the machine and cleaned all the gunk. Hoses are all now free and clear.
2. No kinks on the drain hose, the drain stand pipe is at 35” and is well above 18” from the trap. 
3. Removed the rubber boot from the bottom of machine and cleaned all the gunk
4. Removed the pressure hose, inspected no clogs 
5. Replaced pressure switch with genuine part 
6. Replaced drain pump with aftermarket from Amazon. 
7. Replaced inlet hoses and made sure the filters at the inlet were clean. 
8. Replaced door seal as it had a hole and was leaking 

F21 code still appears 8 out 10 loads. When it appears, if I cancel and then put on spin cycle the machine will drain fine. 

At this point I have no idea what else it could be, could the aftermarket pump be the issuE?