wired ethernet intermittent lost pings

We have 3 MacBookPro 16-inch 2021 M1 Pro computers running Monterey 12.3 with the same issue. They are the only computers on the network with this issue. We have both Mac minis (Mi) and iMacs(non-M1) running Monterey with no issues.

Wired 1gb ethernet will drop connectivity randomly during the day (evidenced by ping) -- anywhere from 3 to 15 seconds at a time, once or twice an hour. We run two simultaneous ping commands -- one to a local gateway and one to an internet location outside of the building. We are on a flat, single fabric dell switched network. This happens regardless of load, and with no programs running interactively. If we switch to wireless, the problem goes away.

We have:

• reinstalled macOS
• installed new cat6 cabling
• tried multiple vendor usb ethernet dongles
• tried installing a local switch (in case there is a power issue)
• tried turning recovery mode off
• booted in safe mode
• tried to follow ping / console to find the offending party
• turned off wireless altogether
• turned off location services (old problem with locationd)
• tried new user accounts
• a lot more that I've forgotten

I really just don't know what else to try.

Any ideas?