Empty chamber after defeating one foe

AshokaMaurya1

There is a painful bug during the wizarding challenge. The forretress allows only one battle with a foe and then it pops an error and says to return to the map. When returned, the chamber is empty and cannot do anything and we are forced to quit, losing a runestone. Till now lost like 6 level 2 dark arts runestones and 4 lvl 3 and 5 lvl 2 care of magical creatures runestones.

Please consider this bug seriously as it is affecting the normal gameplay.