We are having a problem at a sing site. We have gone through a number of RB2011 in the last couple of weeks.

See photos of for damage.

Electricians have installed surge arresters. I sure this is a whole subject in itself and I don't know what spec was installed so might not be correctly spec'd.

And I understand that this does not completely isolate the device from the main but it has been connected to a UPS.

Could this damage result from something feeding back from one of the ethernet ports and not via the PSU?

Seems like something in network. RB2011 has external PSU which typically fails first on bad electricity.

Do you see any burnt components in one of these areas (see attachment)?

I have check all the units and the only visible damage is in the marked locations at the top of the attached image.

Could not see any damage near the ports.

This does not look like failure from the typical surges that you could have from nearby inductive devices or a failing neutral in a 3-phase system.
This first affects the plug power supply which is the only thing in touch with the mains.
It looks more like lightning damage...

It's definitely not lightning. We don't get much of it here.

Any consensus if this is a problems on the power supply or network side?

All PSU have survived each failure, but by capacitor failure location I would assume it's coming from the PSU side?

Any consensus if this is a problems on the power supply or network side?

All PSU have survived each failure, but by capacitor failure location I would assume it's coming from the PSU side?

From information you have provided, it looks like problem is in PSU (powering) side. Unfortunately, without full inspection we are unable to provide additional details. You may write to support@mikrotik.com and refer to this forum post for further investigation.

Any consensus if this is a problems on the power supply or network side?

All PSU have survived each failure, but by capacitor failure location I would assume it's coming from the PSU side?

is one (or more) port(s) connected to equipement that is on another power system? Ground differential could then cause nasty issues....

is one (or more) port(s) connected to equipement that is on another power system? Ground differential could then cause nasty issues....

Normally not, because the ethernet ports are isolated by little transformers that are spec'ed to allow a few kV of voltage differential between the equipment.
Of course this is different when shielded cable is used and the shield is connected at both ends, and also for other ports (serial, USB).

However, even when the entire unit is not at ground potential and is powered by the original supply, the isolation between mains and output in that supply should still protect it against voltage differentials in typical operation. It should also withstand more than a kV.
That is why I mention untypical voltages, like nearby lightning strikes. That can cause voltages that destroy everything.

This one looks more like high humidity of air! Also ionized humidity of air, like a close to beach air!