Random invisible mobs

Been playing on a world and over the last 4 hours I have experienced the following:

• Invisible wither skeleton in fortress hitting and withering me without being visible
• Twice an invisible skeleton actively shooting but unable to be seen by myself - a spider the skeleton hit COULD attack it
• Possibly an invisible creeper

All of these invisible mobs have been completely ghost like with myself unable to attack and mobs - they do not show a hitbox when using F3+B.

VERY concerned