I've been making a Sniffer tutorial for the past week. I had been designing and testing in 1.20-rc1 with having the sniffers on mud on top of hoppers and it was working great. After making the video and getting ready to release it. I noticed that only the farm using grass blocks was still actually producing seeds. All of the other 'diggable' blocks were producing nothing under the same conditions. I even used the /fill command to change the blocks in the farm. If it helps, the video is on Youtube: https://youtu.be/trU_inPplek