Timetable is too small
Sometimes, information does not fit properly inside the default timetable styling.
The height of the cells on the timetable is relative to the time length of the lesson. This relation is controlled by a ratio of minutes to pixels and can be altered by making some changes to a file on the server side.
You'll need to contact Firefly support and let them know that you would like your timetable height ratio increased. The change will take effect overnight.