I'm with kinyongia on the tank- it isn't the source of the problem. I used to breed plenty of veileds in 29 gallon aquaria and they were very healthy. I prefer much larger enclosures nowadays (175 gallon reptariums) for quality of life reasons and outdoor housing reasons, but the tank isn't the problem here.
Personally, I do believe the casque is an early warning symptom for MBD, so I disagree there. I have seen it before. I didn't see what the supplements and schedule for your animal are. Temperature and growth rate is also relevant depending on supplements. You've got uvb, you may need more calcium or d3 in the diet, or may want to slow growth rate down by lowering temperatures available to the lizard to compensate instead. If you live where there is real direct unfiltered sunlight available, 30-60 minutes of sunlight availability a few times a week would be a great idea right now (could be as simple as putting a houseplant next to a south-facing window and opening the window for an hour or so in the warmest part of the day). If not, and if you are using calcium most meals, you may want to raise the amount of d3 via supplements by giving a bit more often.
But the extra d3 might be bad advice depending on what you are already doing. What is your basking temp and supplement schedule?