Traffic marked as unknown in sample bookinfo app


I’m just getting started with istio. A few weeks ago I was able to get it up an running, including the bookinfo app. I looked at the graph in kiali and it looked fine.

However, last night I checked it again and it looks like this:

Initially I thought maybe the sidecar for one of the pods wasn’t running, but I checked and it doesn’t seem to be the case. How do I debug this?