Thanks for the fast reply! I'm using both Tractor Swathing and Swathing+ (I have almost all of your mods installed). I'm on Judith Plains Montana 4X. I just tested on a new save with only Tractor Swathing, Swathing+ & Easy Dev Controls enabled and got the same error.
Judith is one of a handful of maps I have now that I check things but I must have not checked that one when i first made Swathing+. Can confirm, Judith clover is harvest ready at state 4 where my mod is set to look for state 5. Easy fix but I am also looking into another issue and don't want to push another hotfix until I sort that one out.
If you wanna fix it on your end, I could walk you through it pretty easily if you shoot me a message on Discord (username Bbdude)