Could you post a picture ?
Are you using custom content ?
I am having the same problem, I tried changing the saddle, uninstalling all my custom content, everything! Nothing worked! I tried to find help and I couldn't find anything addressing how to fix this. Please help!
It's not cc. Have you ever downloaded something from the exchange? I downloaded some horses and coat colors, and from that day, I have had this glitch. I make my horse clothing options for leading, halter and nothing on its back. It works, but when my sims brush the horse, they change my horse to its naked skin, which has a blanket and I can't change it. I just make them lead my horse after and its fine again. So ya, its not cc. Sadly, it always shows up in horse coat advanced mode, which makes it super hard to edit and create a nice horse coat, but I got used to it and exit and enter advanced mode at least 7 times when making a coat.
Go to game's pitch and the "downloaded content", then try to delete all the blankets
I had this same issue. When you download a horse from the exchange it will sometimes come with a blanket that will conflict with another blanket. Open your launcher, go to installed items, all items tab, let it load and patiently look through all of it, you will find maybe more than one horse blanket, usually marked CAS on the very right hand panel. Delete all blankets that you find. Here is a thread on the sims forum I started about the issue too.
https://forums.thesims.com/en_US/discussion/879829/horse-blanket-issue copy and paste into your browser.
Once they get into your system they are hard as heck to get out. I dislike it very much. Good luck.
