Semester back and backlog are two different things. Here is the detailed information on this topic-
The criteria changes from year to year, so make sure to keep a check on that.
Everyone is given a chance to clear their backlogs during the summer semester.
The rules keep changing with time, so it is better to keep yourself updated on the
latest rules regarding backlogs.
In case you are trapped in any of these situations, do not panic. Try to clear your backlogs. Do not be disheartened and remember that things will eventually get better.