Doesn't look like any big change happened at 9:15, that's for sure.
Thing with the download is as it's bonded, everyone's already load-balanced across all available channels (probably). Hence they can't really do anything about downstream congestion short of installing new equipment (costly, long lead times). Upstream is easier as they can just shift people about.
Ignition would know better, but one of the mods ****ed him off and he's left the forum again
By the way, I recently had a graph that looked like yours, and had similar symptoms - but it turns out it could have been upstream congestion all along. Despite getting pathetic download speeds (5-10mbps) and full upload speeds, as soon as they doubled the upload capacity my download speeds shot up to the full 50mbps. Can't really explain it. Something to do with ACK suppression is my guess.