Party members are loathe to change targets in combat. Once they've locked onto an enemy, even an inaccessible or simply hard-to-reach one (distant, blocked by enemies who keep stabbing you, or whatever), they won't change until that enemy is dead or unconscious (re-entering combat mode doesn't help). The Avatar's target can be changed by double-clicking something else, but that doesn't always work. It helps if you first break the Avatar's combat AI momentarily by manually walking one or two steps.
Same issue here. I've even had cases where all non-avatar party members were crowded against a wall trying to reach an out of reach enemy while they were killed by a monster right next to them.
This has been greatly improved