It's possible that answers for which you received Nice Answer and Good Answer have been deleted. When the badge process runs, it checks to see if you have the correct number of a given type of badge, and only if you have fewer than you should does it award one.
So if a previously marked Nice Answer was deleted, then you met the requirements again, it wouldn't award you with another one until you had more Nice Answers than you have Nice Answer badges.
According to your user page you have 52 answers voted 10 or higher, but 54 Nice Answer Badges.
While your old badges will not be taken away, you will not receive another Nice Answer badge until after you have 55 answers with a vote total of 10 or more.