Turrets from both OpenModularTurrets & from Immersive Engineering don't target certain mobs such as brain slimes as "hostile" when they are clearly hostile.

An issue opened over on OMT's github (with the same issue) has suggested your mobs are somehow not tagged correctly, and therefore certain items such as turrets ignore these mobs.

Could you link that issue for me? I'm curious. Wondering if it's the IMob Interface in which case I cannot implement that sadly.... but maybe he checks something else.

Here you go

although there's not any additional information there unfortunately. This has happened to me with IE turrets as well though.

Although I would not advise him to use isCreatureType to check if a creature is a monster; I might have a solution for this. Thanks!

Update
This still appears to be an issue as of the 1.2.3a release for Primitive mobs, which was just over a year ago.

Can confirm this mobs dont get attacked by any turrets. not openmodular not IE