Proliferation of network calls with long wait times

Hi all! First time post here.

I’ve run a performance profile using WebPageTest. About halfway down the waterfall view, I see a proliferation of white “wait” bars with a duration between 15 and 20 seconds before the network call resolves. I’ve looked through the network calls with these wait bars before them and they all seem to be using HTTP2. My (perhaps incorrect) understanding of HTTP2 is that it will allow for more than 6 simultaneous connections to a single domain, so I don’t understand why there is a buildup of queued/stalled calls. The following is a link to the webpagetest waterfall view in question.

Why do I have a sudden buildup of network calls with a long (>15 seconds) “wait” status?

https://www.webpagetest.org/result/201209_DiNQ_c19183c8bd4bbf27026ea793828127ff/1/details/#waterfall_view_step1

HTTP/2 itself can support hundreds of concurrent requests (in this case it looks like the server advertises 100 as the limit). Chrome has been walking back from that though and has been limiting requests on the client side based on various heuristics because of poor server prioritization support.

If you look at the bandwidth line at the bottom, the connection is saturated until the 17-second mark or so, so having more in-flight won’t help. Likely contention with the video that is loading.