random skeletons stop moving/attacking, and don't burn in daylight

Occassionally in survival, some skeletons stop moving completely; they don't burn in daylight; when hit, damage sound plays, and damage hearts appear, but only the first time they are hit; also, they do not move/are not knocked back when hit; subsequent hits do nothing as though they are not really there; they do not fall when blocks underneath are mined away.

I am new to bug tracker, tried to search to see if this has already been reported but did not find anything.

Thank you for your time and dedication to this great game!