[HR] Unable to mount horse again after Sim resets from horse

For that user, reloading the game caused the Sims to reset and then they couldn't mount anymore. Hence I asked if it was the same other than how it initially started happening.

For the other users, the Sims reset when they loaded back into the game and for you they seem to have reset when something else happened in the game. 

• Reset = Sims abort their interaction and stand back on the ground. Sometimes they do a small T-Pose before doing that.
• Clipping: Sims and objects/other Sims melt into each other or overlap

From your description it sounded like the Sim reset because of what was happening and then just glitched next to the horse which caused them to clip. If I understand you correctly, you still have the mount interaction though ?

Have you tried what happens if you move the family out and back in ? Can you then mount the horse again ?