1) There is no lock on enemy on the controller, so right-click will only put you into sneak mode.
2) The lag in the game is horrible, because it has to pass ESO servers and XBox Live. I can always tell when the kids get out of school because of it.
This lag will affect your target because it'll change, but not be displayed. By the time you continue your attack, the original will remain "locked".
I can understand your frustration, because it's annoying, especially on world bosses and your attacks are going to surrounding wastes of ammo.
There is a solution, though it's not always easy to apply: don't button mash, especially if you're a spellcaster. Stacked attacks will always run their course even as you desperately try to change targets, so slow down a bit and this should help refocus enemies easily.
Note: this logic doesn't apply to group dungeons because everyone bashes buttons and think you're attacking something else.
Click and hold down the right thumbstick longer (clicking will just put you in sneak). It will highlight the target and you'll be able to see them moving around even through walls until they get too far away or stealth.
I'm not 100% this gives a lock on feature though, actually I'm leaning towards it does not. I just use it to keep an eye on who my target is in pvp.
Yea, try a Critical Rush or a Dawnbreaker and hitting a rat.....little *** are tough...
I hate when that happens. So glad there are no random critters in the veteran dungeons.
The targeting issues are very frustrating, too. I once had a fire staff heavy attack go backwards over my shoulder and hit something behind me...
Between that and the invisible enemies, my attacks in my bar are now all AoEs. (She is a healer primarily, so I can get away with that, because she is generally DPSing during trash mobs and healing during bosses, so doesn't really need single target skills to do well).