The bug
The coordinates of the sniffer "minecraft:sniffer_explored_positions" tag do not check the dimension.
Reproduce steps
Create a grass block platform in the overworld and nether.
/fill 7 128 0 4 128 4 minecraft:grass_block destroy
Summon a sniffer on the overworld platform.
Add the coordinates of all the grass blocks on the platform to the locations excavated by the sniffers in their memories.
/data merge entity @e[type=minecraft:sniffer,limit=1] {Brain:{memories:{"minecraft:sniff_cooldown":{value:{},ttl:0L},"minecraft:sniffer_explored_positions":{value:[[I;7,128,0],[I;7,128,1],[I;7,128,2],[I;7,128,3],[I;7,128,4],[I;6,128,0],[I;6,128,1],[I;6,128,2],[I;6,128,3],[I;6,128,4],[I;5,128,0],[I;5,128,1],[I;5,128,2],[I;5,128,3],[I;5,128,4],[I;4,128,0],[I;4,128,1],[I;4,128,2],[I;4,128,3],[I;4,128,4]]}}}}
Teleporting the sniffers to the nether platform.
/execute as @e[type=minecraft:sniffer,limit=1,distance=..5] in minecraft:the_nether run teleport 6 130 2
Found out that sniffers do not dig in overworld and nether with the same coordinates.
Fixing this requires a slightformat change:
Following this format directly will also make it consistent with other position memories (such as villager homes, bee nests, etc.)