Not sure if this would fall under training issues, but my TB Rocket has become increasingly girthy since I have owned him. When I first rode him I thought it was because I was using the 15 year old girth that came with my 15 year old saddle and it would kinda bunch up on the sides as I rode no matter how I did it up. I have since then replaced it with a cloth like girth that does not bunch up and have been using it for about three weeks now.
He is still extremely girth though. It's not like I crank up all at once either or even ride it with it very tight. I will barely tigthen it when I first saddle him then walk him to the ring and then tighten it again before I walk him to the mounting block. I have to make sure to have either him crosstied good or the flash noseband done up because he will whip his head around and try to bite me.
Any suggestions would be great, I have checked him over for girth sores and he doesn't have any and doesnt mind just being touched in that area. His saddle also fits fine. My trainer suggested that maybe its because he is still a little bit underweight and doesnt like it being tigthened on his ribs, but I dunno.