After performing a successful update of all hosts to 6.7.3, following VMWare procedures, NSX is not working anymore.
Searching for possible cause, I then found a VMWare article saying that the update process on an environment with NSX has a few constraints.
Unfortunately these are not mentioned in the update procedure from ESXi.
The issue seems to be that new NSX VIBs need to be installed on the hosts as there's interoperability issues amongst versions of NSX and vSphere hypervisor (ESXi)
The question I've got now is if I can still upgrade the NSX VIBs now that all hosts have been already updated and the issue is already happening.
Can you till us please which NSX version and vCenter version you have ? If it is supported you should be able to go to "Host preparation" and click "Resolve" on cluster level or host level and you should see "GREEN" checkmarks again.
Please share any error message or screenshot if possible.