What are some common mistakes students make with dynamic equilibrium?
I would say one common error is not emphasizing the fact that there are two processes (a forward and a reverse) which are both happening at the same time at equal rates.
The video below shows water which has salt added to the point where a saturated solution is created. Then more salt is added, a dynamic equilibrium will be established between the processes of dissolving and crystallization.
Video from: Noel Pauller
Hope this helps!