When my pokemon faint, my game crashes and restarts me from my last save.
same thing happened to me
Version: 1.1.15 Windows
Description: Experienced in Gyms (multiple, most recently Vipik Gym Leader) and tested in the wild with random trainers and pokemon.
Recreated with parties of 1 pokemon as well as parties of 2-6 (all active pokemon). Have tried combinations of item usage and consumables to no effect to verify it wasn't a miscellaneous bug with a certain held item.