I think the problem is PB&J (aka mud and blood sandwitch). Jam probably has lot of simple sugar that will spike his insulin level about 5 to 10 minutes after eating it. Then all that insulin will work to metabolize the sugar but no new sugar is coming into the blood stream and his glucose level in his bloodstream crashes. So when he comes home basically he has bonked. Your brain can only run on glucose not on fat or anything else and the lack of glucose is causing his brain to want to sleep.

Suggest he snack on boiled potato instead and graze during a ride instead of eating ton of sugar all at once. See if he still does the same thing.

I've been warned many times over about the "danger" of eating high sugar food during a road event. If you know you have a sprint finish, load up on simple sugar about 5 minutes before the finish. That is what I've been told.