I plugged up the middle of the lower sieve in wheat in ‘22
95% of the middle was plugged tight.
Found it when getting ready for soybeans that summer.
The last 20% were really thick with waterhemp. 
How much wheat did I lose?
No sensors for the middle.
Once it starts building up it will not start cleaning out.
In your case, you probably have to climb inside of the machine to actually see inside of the left walker.