Sj is right to much calcium is as just as bad as not enough,regardless of brand.
Which is why we stress using a well known staple diet like Critter Love or Bml which have a measured amount of calcium evenly distributed through out the staple, rather than "sprinkling on" irregular unmeasured amounts of calcium.
If you are using a well known, tested, widely used diet and follow the directions and use the ingredients specified there is no need to add anything extra to it.
As Sj suggested ease up on the treats especially in the afternoon so when they wake up they are hungry.
What diet are you feeding, what fruit and veg are you feeding, how are you preparing it, how are you serving it, how old are the gliders, what time are you putting the food in the cage, what time are you taking it out of the cage... many things can affect a gliders eating habits besides the diet itself.
Vets can be wrong, especially about diets. I use 3 different vets, all have different knowledge levels of glider diets, none of which I agree with or take diet advice from. Vets aren't dietitians.
Please keep in mind most vets don't see gliders enough in their facilities to have even general knowledge and experience with gliders as much as they do with domestic animals. They also don't really understand the glider community and how it networks nor do they follow the glider community as a resource for current accurate information. Much of a vets info regarding diet is old and sometimes completely inaccurate.