Why do I need to reset my xbee?

I am using Xbee pro 900 hp s3b for a digimesh network. After several hours of my network communicating, 1 of the xbees lost communication with my coordinator. The only way to bring it back was a power cycle. What would be the reasons that my xbee loses comms with the coordinator?

overflow? any others?

Voltage level, current draw, buffer overruns, invalid API frames. Etc.