Not sure if that's the cause, but it very well could be. I'd avoid Kaytee food of any kind. The best is Mazuri or Harlan lab blocks. Or Purina LabDiet.
Check a local feed store for lab blocks, its MUCH cheaper that way than buying from a pet store. A good feed store if they stock them should also sell out of a big bag in smaller quantities, like 5 or 10 lbs. Most pet stores sell Kaytee lab blocks which are very poor quality and they use a cancer causing preservative. Plus at pet stores lab blocks are like 1.50 to 2.00 a lb or even worse. Petsmart wants like 3.00 a lb for mazuri. At a feed store or reptile show it's more like .40 a lb if you get a whole bag or maybe .75 per lb if you buy smaller quantities. Mazuri has a shelf life of 9 months and Harlan 6 months. You can freeze it and it will last another 6 months or so.
Seed mixes don't really have the proper nutrition, especially for breeding mice, plus they pick and choose only the bits that they want and don't get the nutrition they need.
If you don't see it out for sale at the reptile show ask the feeder breeders, somebody should have it. If you have a choice get Harlan 2018 or 8604, if not then Mazuri 6F or 9F breeder block are good as well.
Mazuri has a lower protein content than the Harlan formulas I listed. Mazuri 6f is 16% protein 6% fat. 9F is 16%/9%. Harlan 2018 is 18%/5% and 8604 is 22%/5%.
If this is solely for mice then the best is probably 8604, for rats 2018 is better. All of them are good though, and any would be much better than any Kaytee food.
It's really a shame that pretty much every pet store sells Kaytee food when it is of such poor quality.
Until you can get the lab blocks you might want to feed more of the dog kibble than the seed mix.
...but she is my kid, and I made a promise...