1. Insufficient Fermentation: The production of BBQ pork buns needs to undergo a full fermentation process, and if the fermentation is insufficient, the baked BBQ pork buns will be flattened.

2. Uneven rolling: when making barbecue pork buns, you need to roll the dough into an even thickness, if the rolling is uneven, it will lead to the baked barbecue pork buns appear flat phenomenon.

3. The filling is put on the wrong side: when wrapping the barbecue pork buns, you need to put the filling in the middle of the dough, if the filling is put on the wrong side, it will lead to the shape of the baked barbecue pork buns is not correct.

4. Insufficient baking time: BBQ pork buns need enough baking time to be fully cooked, if the baking time is insufficient, it will lead to baked BBQ pork buns flat.

5. Baking temperature is too high: in the baking of barbecue pork buns, you need to properly control the baking temperature, if the temperature is too high, it will lead to baked barbecue pork buns flat.