The Bug:

Despite being a "sniffer_diggable" block in the code, Sniffers will never dig in normal mud blocks. They will dig in muddy mangrove roots, but despite searching and sniffing on mud blocks, they will never actually dig for seeds.

I suspect this may be because the mud block isn't technically a full block; you sink down a bit in it. This may mess up something with the Sniffer's block detection. Muddy Mangrove Roots, for comparison, are a normal full sized block.

This behavior can be observed here:
SnifferMud.mp4

Steps to Reproduce:

1. Spawn many Sniffers on multiple platforms of "sniffer_diggable" blocks, including normal Mud
2. Wait for them to dig for seeds
3. Take note of how all will, except for those on normal Mud Blocks.