yes is partly related to the last DLC. Straw Harevst added 7 new fill types to the game and it seems to have pushed a lot of players past the 255 base game limit for fill types.
Swathing sorghum adds another fill type and if other mods are causing the game to exceed 255, than Swathing+ will not have its needed fill types to work. This also causes a handful of other issues too.
To fix it, try installing my new mod FillType Extender, this will allow the game to have 511 fill types. Let me know if that still doesnt fix it!