Sniffers will never track or dig into soil with a non-solid block on top. This can cause them to not look for seeds at all in snow biomes.
To reproduce, use the following superflat world and spawn a few sniffers:
minecraft:bedrock,2*minecraft:dirt,minecraft:grass_block,minecraft:grass;minecraft:plains
In 1.19.4 Pre-3
[media]This works with any type of non-solid block, even stuff like grass or flowers: