Proliferation of network calls with long wait times

[mike.ample]

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/20120...view_step1