I am having the same exact issue.
However, it is only the produce from seed packets (not from harvesting or being gifted) that will not sell.
This is a massive chore because if you buy seed packets, the only way to get rid of the piles and piles of produce from your inventory is to place them all individually on the ground and delete it with the sledgehammer tool in build/buy mode. But you may have hundreds of individual produce items at that point. Not a good option, but the only thing I've found so far to work around this bug.
