The SDK is again the answer to your question - although I don't have a great answer for you yet.... do you have any experience in C++? If so it'd definitely be worth you downloading the code, building it, and adding some debug info so you can figure out exactly what is happening in your case.
The possibilities I've found so far, in increasing order of likeliness:
- The ignored enemies have "notarget" = "1" in it's spawnArgs - this causes idAI::ReactTo to ignore them until they have been attacked. I suspect this isn't your issue though since the default notarget seems to be "0".
- your turret is "dormant". It looks like AI's are usually dormant until they're woken up by a player (not monster) being near (based on idEntity::DoDormantTests). Try setting "neverDormant" to "1" in the spawnArgs.
- There's something else that I've missed that would cause it to ignore it's enemies. Using C++ I'd debug this by putting a breakpoint / logging into rvMonsterTurret::State_Combat and see if it's selecting an enemy. If it isn't, then debug into CheckForEnemy to figure out why that isn't finding one when you think there should be.