Yeah
Only excuse is that Elbaf is THAT big and they are far away
Or the HK can hide away their presence
but yeah COO is not really consistent
Luffy and Zoro could sense Loki haki far away even thought he was chained up with seastones who even stop someone from using haki.
There are four options:
1. Only characters with a insane haki can be sensed. A reason why Luffy or Zoro didn't feel Lucci or Kaku since they are not really threats.
However guys like Saturn, Kizaru or Loki pose insane haki, that is a reason why Luffy could sense them. Like why you even need sense CoO for fodder.
2. Pranks and Gunko pose not a great haki threat, a reason why Luffy feelt Loki but not these two, they don't pose the insane haki to been see as threat.
3. Holyknights are like Assassines, can hide their haki, so no one can sense them even with CoO.
4. Oda just doesn't care....
Choose one.