For about the first minute after installing Network Observability, it displays "Unable to get overview" in Observe > Network Traffic (see screenshot).  It appears it is still starting up.  After some time, everything works as expected.

While the issue does goes away and is ultimately harmless, it leads to confusion when you see the error page.

1. Install Network Observability.
2. Create FlowCollector instance.  Refresh web page when the dialog comes up.
3. Go to Observe > Network Traffic.  There is an error that says "Unable to get overview" and a 400 error.

Error page

Graphs should appear