It looks like it currently only has one horse registered to it, actually. And the horses you're using to fill it are Vanners, whose skill sets aren't suited to Show Jumping comps; they'll be dragging the prestige down a bit.

I would personally set it as reserved for Selle Français; they're the best SJ breed, so they'll have good skill sets to boost the prestige. That's what I have my comp reserved for, and it runs frequently without issue. Several other top SJ comps are also reserved for Selles.

I'd then spend a while entering Selles in the comp to get it running again, until it gets its rosette back. Then I'd boost the difficulty to 85% or more, to make sure you're only getting higher skill horses entering, and that way its prestige can continue rising.
You might want to get two high level Selle skillers to continue filling it for a while, until its prestige gets to 80% or more, and you can safely let it run on its own. It shouldn't cost much; Selles are one of the cheapest breeds to get skillers for, usually less than 100 passes to get a high level pair. Even cheaper, if you buy Teared foals and skill them yourself.

This also isn't necessarily the result of you doing anything wrong in running the comp. Sometimes comps can run smoothly on their own for months, and then just have a brief hiccup where they don't run for a week. Usually just means there's less activity in that comp type, or that your comp accidentally got passed over in the comp list. It can happen even if the comp's settings are ideal.
If you manage to get the comp's prestige up to well above 75%, then it'll be less likely to lose its rosette anytime it has momentary difficulty running in future.

Yes there's only one horse in there and its not yours. I agree with Avre. Do not use vanners for show jumping they are better at cross country because they excel in stamina not speed.

Selles are the best showjumpers but I also use shetlands as they are quite good for prestige as well

Thank you so much for the comments I'm changing my strategy then