I’ve noticed that sometimes WPT waterfall shows requests in the order that does not seem to be the order in which the requests are issued by the browser.
For example here:
Item 2 in waterfall is HTTP/2 Stream: 7 (as you can see response comes last)
Item 3 in waterfall is HTTP/2 Stream: 3
Item 4 in waterfall is HTTP/2 Stream: 1 (as you can see it is the only one with DNS+TCP+TLS before)
Item 5 in waterfall is HTTP/2 Stream: 5
They all have the same request start time (coming from ) and this is probably why – AFAIU requests are sorted by start time, but if multiple start at the same time, they get wrongly shuffled.