Tracking data transmission errors

Hello, I have a greenhouse in the backyard and I’m keeping track of a few temperatures by using an xbee to transmit the data to a server in my basement. The server, via it’s xbee, asks the greenhouse for the temperatures every five minutes. If the data comes back and is incomplete, then I record the event as an error, then ask again. I’ve been running it for ~6 days straight so far, and I have ~1800 events recorded in my db, and ~800 errors. I made a bar chart of the number of errors by time of day (see the attached pdf).

I found it very interesting that almost all my errors occur in the middle of the day. I have zero errors after 5 pm. Where I live the sun has been going down at 4:30.

Does anyone have any idea about why I get so many data transmission errors during the day, and so few at night?