The “Overseeding” policy in the Town Center is bugged. It does not +25% yield to any crops.
In this example I enabled the policy at the start of year 56, and disabled at the start of 60. Graph looks the same for greens, hay, grain, etc. No crop yields were affected.
I think it still does +25% fertility loss, but I didn’t really notice with all the late game composting I already have setup.
I tested activating the “Hair of Saint Hadia” relic at the temple, and that one does increase flax yields by 50% correctly, so the problem appears to be specific to the “Overseeding” policy.
Savegame where this happened: https://drive.google.com/file/d/1lzrBOuDQA4d0dcQaxCr9Y3iSZ0JWs_8z/view?usp=drive_link
Had to upload it to google drive because the zip was over 4MB couldn’t post it here directly.