[Minerva 80 high ident in one zone]

Are you checking the voltage across the terminals with the loop connected? 

You should be getting 24v output across all 4 loops with nothing connected.

If you are getting 16v with nothing connected then this is way too low and you're looking at a faulty main board.

The detectors will work within certain ranges, but your panel will start registering all sorts of weird and wonderful issues if its only outputting 16v. 

If you're getting 24v with nothing connected you're going to have to start splitting the loop and measuring the voltage at the detectors until you find where the drop is, and that will be your fault.

 

Ive attached a pdf that should explain quite a few things for you too

 

Minerva Addressable Service Instructions.pdf

[Minerva 80 high ident in one zone]

The system basically adjusts the range in sensitivity of a detector due to dirt/age to reduce false alarms, so after a period of time that threshold will rise to compensate for a 'dirty' chamber.

When you replace a head that value is obviously way higher as the new detector is cleaner.

Defaulting the threshold is telling the panel your detector is clean

 

I think its under 3.9 something in the menu. Best bet is to download a manual for it if you dont have one

[Minerva 80 high ident in one zone]

Theres also every chance it could be a faulty base or bad connetion drawing too much current.

I would also do a reset point threshold comp. any time you change a device

[Minerva 80 high ident in one zone]

You wont get high ident faults on mcp's mate, i wouldnt even bother looking there. 

It certainly looks like the air quality is being affected and this is whats triggering the faults.

Could you change the type of detectors to co or heats? That would resolve the issue, other than that, some sort of barrier at the door or extractor fan

[Minerva 80 high ident in one zone]

If you're experiencing these faults when you open the door and expose the area to dramatic changes in air pressure and quality, i would say that is exactly whats causing the fault, im guessing you only have these activations on optical smokes?

[Minerva 80 high ident in one zone]

Any high ident faults ive ever came across just meant the heads needed a good clean. Take them down and give them a good blast with a can of compressed air and make sure the terminals are clean as well