A neutral and ground reversal should not be there, Some equipment has a max voltage above ground that it can be floated. With some of the instruments I used that voltage was around 30 V.
What caused some of our researchers and me considerable grief is when a ground bond on a single outlet in an outlet strip came undone. What this can do is put about 60 VAC on one of the grounds, You might say, what? Where does the 60 VAC come from?
Many power line filters use a symmetric impedance to ground, hence it turns into an AC voltage divider with the center disconnected which will supply very little current. Now that can become a reference from another instrument and....something breaks.
If stuff i wired right, that 4V should not matter, but I d think it is excessive especially with RS232 running around. If you don't already INSIST that he bench be wired with isolated ground receptacles or at least a few of them.
This is one of those questions that knowing what part of the world your in helps a little. In the US, ISOLATED ground receptacles will run the ground all the way back to the building ground reference where it is very clean. The receptacle will be orange. A building might get wired with bx strung through metal studs without the insulating bushing and you get "yuk" as far as a ground is concerned.
I've used the ONEAC power conditioners
https://www.powervar.com/power-conditioners/ (the single phase ones) on a very critical measurement system. At one point the measurement system was based on a Mac Centris and the hard drive never crashed in the 16 years of operation. Reliability went up a lot with the older system and it was continued to the replacement system. I used a 1200-1500 W conditioner and a ISOBAR surge suppressor. Management never directly sees the benefit as a bean.