This is certainly NOT connected to the trainer but the patch which reset the graphic options by default. Try the "mouse trail" fix if nothing else helps, google is your friend 🤐
Toggle on and the trainer keeps your Health, Stamina, and DeadEye at max, as well as max for the horse.
this likely has nothing to do with the trainer..
It turned out that the feature doesn't work at 144hz monitor refresh rate, I had the same problem, switched to 60hz mode and now it works fine.