Sniffers no longer avoid digging up locations they have previously digged up

The bug

Sniffers no longer avoid digging up locations they have previously digged up.

Reproduce steps

1. Create a grass block platform in the overworld.

   /fill 7 128 0 4 128 4 minecraft:grass_block destroy

2. Summon a sniffer on the overworld platform.
3. 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]]}}}}

4. Found that after a while sniffers still started digging.