Game Mechanics: Weird auto-attack bug

[Noselacri]

Today I keep getting hit by this strange bug. It makes me unable to auto-attack, and mob health bars don't move either despite clearly taking damage from other sources. Happened repeatedly in Upper Guk while in a group, with no visible cause or solution, and would just go away again after a while each time. I would target a mob that everyone else was fighting, activate auto-attack, and no swings would occur. When moving out of range, I would get the "target is out of range, get closer!" prompt, but nothing at all would happen when in range. It wasn't latency, everything else was fine and no signs of lagging.