So VMware have admitted that the alert seen in vROps 6 for the below error and have a KB article written for it.
Unfortunately the resolution says to disable the DVPortGroup Dropped Packets alert, this turns out to be easier said than done.
As an alternative fix I have looked at the configuration for the Alert Definition to allow people to delete the current alert and re-create it if\when vROps 6.0.x comes out and the fix is present there.
Prior to deleting the Alert definition go to the alert and take a note of the text for the alert “One of more ports are experiencing network contention” because we are going to use that to recreate the alert definition at a later time.
Click on the Content tab (2nd from right) and click on the Alert Definitions
Now you have two options here.
1. Delete the Alert Definition (simply hit the red X to delete)
2. Create the Alert Definition if you previously deleted it.
The following instructions assume you have deleted the alert and want to recreate it.
Click on the Green + to create a new Alert Definition.
Paste the name that was previously saved “One of more ports are experiencing network contention" in to the Name box.
Next we need to choose the correct Base Object Type
Click vCenter Adapter
Click vSphere Distributed Port Group
Change the Alert Impact to Health, Critical, Network: Performance, 1 and 1
Select “Port is experiencing dropped packets”
Drag it to the Symptoms area in the main screen.
Select “Check if the packet drops are…” text
And drag it to the Recommendations area in the main screen.
Click Save and the new alert has now been created and new alerts based on the criteria will show back up again.