I have this issue for quite a long time, looks like it is still there.
OPNsense 18.7.10-amd64
Reporting - Insight: No data available
I like graphics. What I'm doing wrong?
What's your configuration like regarding Netflow?
I took a screenshot.
I changed the setting for LAN to LAN instead of WAN,LAN and it seems to work now.
:)