From my understanding, it metabolizes differently in every person. It could be a crash or could be that he is just “hangry” (so hungry he gets angry) once his meds have worn off. Every person is so different in how their body handles the medication. What did the doctor say?
We used to have a crash once home as well and it varied day to day on how severe it was. Our doctor changed up the way we took the medication and that helped with the crash. If it is from hunger, maybe move dinner up or snack? It is so difficult to navigate med changes. Good luck!