I have 4 sniffers in a 12x16 block pen that has grass and moss blocks with a minecart hopper running underneath in a meadow biome. I have two more sniffers on leads on grass to test if they will search for seeds also.  Not a single sniffer has searched for seeds in over 8 hours of game time. Is it possible the biome is too cold?  It is also a bedrock realm.