The glue joint for the two pieces of the manifold failed when it struck the tent's tarp. Estes warns don't use too much glue. I say don't use too little!

Very likely failed upon impact with the ground (a tent canvas really) and not during flight.  Video clearly shows it still attached during staging.  Estes instructions warn of using too much glue which would clog the three pasages, but I am certianly going to use more glue when I repair it.  This type of plastic, which appears to be a thermo-setting type, may not adhere well using traditional plastic model cement.  I will consider using epoxy or CA or other type glue, or a combination of those to get a truly good joint.  I don't recall what Estes recommended but I don't believe they were very specific about the type of glue used.

Note on the fin's trailing edge (protruding out to the right) the finger mark. This shows how much soot this booster stage collected after a single flight.