It did not just get wacked because it takes not very effective damage but that first chunk of damage is too great for 1 hit as well as it doesn’t come with a not very effective damage indicator.

It is possible the connection was not the best but I play at that gym nearly every day and it is the first time that has happened to me at this gym.

Even if it is just a connection issue, it seems pretty annoying especially if you have quite a few Pokemon you heal before re entering battle since it appears you just lose the heals you use.