I only give BSFL and pupae and flies to my rescue (Fluffy the Water Skink) and she's pooing very reqularly, but I do mix in some mealworm lavae or pupae , or some superworm meat too.
I would hypothesis that perhaps a few issues are coming into play for your dragon,
>> it's maturing and it's metabolic rate is becoming slower
>> temperatures may be an issue (impacts on metabolic rate)
>> no "roughage" in BSFL (very soft exoskeletons c/- crickets)
I suggest checking the daytime zone temperatures, and night-time temperatures.
Introducing some crickets / roaches / locusts into the diet.