What's going on with my freezer?

As you can see from the attached graph there are some major temperature fluctuations. We noticed about a month ago the our GE bottom freezer fridge was melting the ice we put in the ice tray. I thought the kids were leaving the door open and it was thawing a bit, but that wasn't the case. I have been out of town since starting to monitor the temps and will be back today. I plan to inspect the freezer for any build up of ice or anything out of the ordinary. Note the fluctuations are probably more dramatic as we removed everything from the freezer. Any ideas on what could be wrong or what I could do to troubleshoot? Thanks