Air Pressure Aft Filter in WC -Man

To check, run it without the air filter. Also if your mechanic is very heavy handed with the K+N oil, it can clog the sensor. If it's not the air filter, change the sensor. I usually see 5 or less.......

Beware, what your mechanic is saying clashes with the explanation given by v10builder1.
Now, I can't be positive about which of these alternatives is correct, but certainly the latter makes good sense.

And I wouldn't rely on the fact that one display shows '-1' to deduct that the value is supposed to be negative, either.
One inch WC is less than 0.04 psi, i.e. close to nothing. So, the defective sensor could well be the stbd one, which isn't reading anything.
Pulling the filters as CJ suggested should give you a good baseline, anyway.

I've also seen filters that looked perfect, but were totally clogged. You can only clean them so many times and they eventually will implode into themselves at cruise.

Definitely sensor or connector.

Inches of WC is an English unit - not metric. The browser (Chrome) I user only shows a piece of the post #1 photo - what I see I believe to be the starboard engine showing running RPM with 19 in. WC and a green bar under the 19 - apparently indicating the value is OK, but as posted by Fiammetta42, best practice is to record the value with new air filters (19 in. WC is 47.1 millibars).

Common sense will tell you that there will be suction, not be positive pressure, immediately downstream of the air filter with the engine running.

The values seen on the displays with the engines off may or may not be relevant depending on the program/programmer, but the value seen at the sensor with the engine off would be 0 in. WC, -1 is close enough.

To restate what has been said before, the voltages and currents used in these sensor circuits are often very small, so connections are critical. The sensor environment is not too extreme, but salty air is what it is. Hope for a wire/connection issue - might be practical to test sensor by swap.

There ya go. Our new MAN tech.