Are your condenser fans momentarily dropping off?

Are there any radio transmitters on or near the roof, including cell phone antennas? Are there building engineers or maintenance people with older, 2-way radios? SMR ('trunked'), microwave or any older radio system in use near by? - some municipalities use them for their maintenance fleet. They run on 800 & 900mhz, which can cause interference on some solid state systems.

Are there light rail tracks near by, heavy VFD use? Any heavy equipment that cycles on and off in the building? Are there power problems? Do you have 'dirty' power at this building?

Is the battery in the PSIO older than 5years?

It does sound like something is going in the control circuits, and not a 'real' pressure issue.

/Yep, I've seen first hand an old (cir1995) trunked Kenwood 2-way radio temporarily scramble an EXV board for the flowtronic EXVs on an older 30GT.

//grasping for straws?