i have experienced with this kind of situation before, but since i'm a consultant for clients who will/or uses ExtraHop, the questions are usually thrown at me, so what i did was, well I tried to explain them with simple cases like HTML what are the metrics for HTML that we need to take a more closer look; like HTTP Errors 5xx, or sometimes we can compare the HTML request to HTML responses, if there were too many differences in the comparison between request and response it might be, that the web servers are having an issue(s), or we can take a look metrics like TCP response time out (RTO) or High latency, start there then see metrics like zero windows in/out or TCP Resets.
There are many case studies provided by ExtraHop in their website. at first, i start from there, and then I took the time to watch the Tutorial Videos made provided, it certainly help a lot. you can find it in Youtube or Training Videos.
CMIIW. Cheers.... (sorry for the bad english)