Well, I've come across a super annoying glitch last night. So, I set up camp to craft some bullets and cook some Big Game Meat. After I was done, I figured I'd set up a tent and sleep since it was raining. Arthur sets his tent up, and I notice in the cutscene my white horse (named Epona, almost maxed out. almost fully bonded) has changed to a Tennessee Walker. I don't think anything of it. Time goes forward, I get out of my tent, and the Tennessee Walker is still there. A Level One Tennessee Walker. So, I ride to the stable in Valentine to see if maybe my Epona was there. Nope. Just the Tennessee Walker I boarded there from the beginning of the game when I first got Epona.
So, I searched online. Apparently this is happening to quite a few people. Some have lost their pre-order War Horse, others have lost horses they spent $1000 on. Some people have even had all their money or weapons disappear when this happens. I stopped playing for the night, being aggravated. I'm going to play tonight, but I really hope Rockstar is working on a fix for this.