ThinOS 5070 Looses Connectivity for a time RDP/WMS/ENOTFOUND/Missed HeartBeat Threshold

We've a long standing issue with some office based Dell Wyse 5070's loosing connection, not all machines at once, it appears randomly across our office machines.
Some of the errors are missed heartbeat threshold, but also noticing ENOTFOUND at the time and it's looking like after 30-60mins and sometimes after a restart machine starts communicating again.  During the time of the problem it's only possible to ping local loopback address.

ping of the switch attached to was possible but not default gateway, therefore no external addresses were reachable during the duration of the issue. Moving switch port didn’t help.
However if we changed to a static IP on the Dell Wyse it then worked to fix the transport of the traffic and could get to the gateway and beyond, which is strange because the MAC address would not have changed as a result.

Really just raising this as a late stage effort to troubleshooting.  If anyone has any ideas on this your feedback would be most welcome.
Thanks