Forum user Capt. Hunt has reported that the sound / visual effects for the fairings and decouplers don't seem to be triggered consistently.

I suspect that changes to the effect definitions since 0.90~1.0.x may be the cause of the problem.

Details from Capt. Hunt:

Ok, so, just to recap I had two issues with these guys:

First, if adapter and fairings are in the same stage, only the adapter decoupler fires. It does play a sound and there is some smoke effect, but that might just be from the adapter, I can't tell if the fairings do anything.

The second issue was that only one fairing released via staging or action group if the fairings were placed with symmetry, unfortunatly, while this was happening all the time before, I can't get it to reproduce now to verify your questions , but if I recall correctly, it also played the sound and VFX, but that was likely just the one that decoupled. the stuck fairing also behaved normally when I decoupled it with the right click menu.

@Starwaster, I believe you're already aware that the second issue can't really be solved/reproduced, but any thoughts on the first one?

@Starwaster has confirmed that the sound and FX are missing from the Pod Boost Protect Cover and the Side Fairings, and are only present on the Adapter.

Perhaps KSP isn't recognizing the derivative decoupler PartModules used on the affected parts?

Yep, AnimatedDecouplers seems to be the cause of the issue. @Starwaster is investigating.

@Starwaster has fixed the issue by updating AnimatedDecouplers to 1.2.2, and Capt. Hunt has confirmed that the fix works properly as intended.