I have one horse that is a queen jumper (she'll win champion without a doubt) but occasionally she goes through phases where she full-speed charges down the fence. I figure it goes into overcompensation as well as having different riders work with her occasionally, but it doesn't matter what height the jump is when she gets into rushing fences when she's set her mind to it. They could be cross rails or 3' oxers. She's better when trotting in (although still sometimes starts hopping the rest of the way) and when like this, nearly always rushes when cantering in. Trot poles and placing poles haven't done as much as desired in helping prevent this. She does better with grid work and bounces, especially cavaletti bounces after a fence, to back her off, as well as halts on the straight-away. However, it seems to all go out the window with a long-approach single or line.
I don't have this issue with my other horses, and it's been a long-standing on & off one with this one rescue OTTB who we've had forever. No medical problems that are obvious, her on & off phases do not correlate to any female 'season' cycles as they'll last a few months at a time, and we do plenty of pole work, alongside extension and collection. Perfect on the flat, and perfect with jumper roll-backs and short approaches to fences, but single fences and lines can get questionable fast. It's always a work in progress with this mare keeping the balance of not over-jumping her (she's 18 this year) but keeping her in enough shape along with mental workouts to help prevent her rushing.
She's been doing marvelously better in general behavior since learning from this online university and working with a Dually halter (she didn't have very good ground manners stemming back from her racing and rescue days), and she has terrible herd separation anxiety if left alone, as well as general anxiety as the bottom of the herd pecking order.