It’s amazing how much is going on when you dig through logs. On this occasion I was looking at “tasks & events” of a host and noticed a lot of network errors.
Alarm ‘Network uplink redundancy lost’ on triggered an action
The error was occurring every 5 minutes. This was made visual with the use of Log Insight. My new favourite tool.
I couldn’t find anything wrong with this particular ESXi host, vSwitch or uplink. It had the same configuration as all the other hosts in the cluster.
The fix was to go to the top level where the alarm is defined, Edit Settings, disable the alarm, then go back and re-enable it.
After that, the errors stopped appearing.