Invisible Skeletons

I opened a survival map and after a while got to mining
I first saw several mobs but after killing them there was a skeleton shooting arrows and it was invisible then it started shooting arrows which goes throug me without giving me damage and when I tried to hit it (still invisible just predicting where it is from arrows on the air) no damage given either

I don't know how to reproduce this as it just happened when I was mining
Doesn't happen every time though