The creature assigned in the Daily Monster quest does not always appear in DM. This seems to happen when the creature to kill is relatively low level for the player. For instance, balrog does not show up to 597 lvl players even if it is given as daily quest.
Anonymous
If the daily monster appears within the first 10 spawned enemies, there will not be an 11th. I have heard of cases where balrog may not appear if there is not enough space detected for spawn which was affected by corpses. But I don't know if that bug was fixed.