(During solo play) .. If two sets of hostile NPCs (eg. sinecure and mockery) spawn next to each other and start fighting. They will immediately know where the player is and sometimes prioritise the player over each other. This will happen even if out-of-sight or crouched or the player has yet to join the fight.
Even if they don't focus on the player initially, as soon as one side wins, the rest of them run towards the player.
On multiple occasions, I've been sneaking about then suddenly I get charged by a pack of sinecure from out of sight, just because they spotted a corrupted creature/mockery... and apparently, they both think it's my fault.