So you have 8 identical setups for your 8 beardies which are all from the same clutch and only one has failed to grow at all since a hatchling in the span of 7 months? And the other 7 in identical setups are all sub-adult size?
Pardon the bluntness but many of us have been doing this for years if not decades and can tell when something isn't right. We are here to help. I assume since you posted here that you are seeking help and want what is best for your dragon, that's what we want too. The only way that will happen is if you are honest with us so we can help.
Can you post a picture of your setup for this specific dragon? We understand what your question is. But what we are trying to tell you is that this isn't a type of food issue. It's a 'why is the dragon not eating on it's own' issue.
In your profile you state that your enclosure size is 12x10x15. You've been using CM this whole time, if that's the case this enclosure is too small even for a hatchling. If these dimensions are in inches it is still too small.
In your profile you state that your basking bulb is an LED bulb. LED's produce very little heat, if even noticeable heat at all. LED's are not suitable basking bulbs for the simple reason that a basking bulbs main purpose is to produce heat for the basking surface.
Without proper heat, your dragon isn't going to digest any food. IF the dragon is not digesting food any food it eats is not going to be absorbed. If the dragon isn't absorbing nutrients from it's food, it will get sick and be lethargic, and it won't want to eat.
Point being is even if you force feed your dragon the healthiest diet in the world, if he's not able to digest and absorb it, nothing will change.
Husbandry needs to be fixed first for diet to start having a healing affect.
-Brandon