In some areas, a wizard will have trouble moving around. Things will lag, freeze, start, stop, etc. The problem is caused by some difficulty that involves the quest arrow/helper system.
The solution is to turn off the quest arrow (pressing "T" toggles the arrow on and off). You can still use the arrow, but you need to come to a stop, turn on the arrow to get your bearings, then turn the arrow back off, then continue on your way.
Fortunately, this only happens in a few areas, and most of the time you can have the arrow on without any problems.
If turning off the arrow doesn't solve the problem, send in a ticket to Support.