XBee Pro900HP Firmware version 8070
Module sends and receives data in API mode for approx 35 hours, with occasional communication failures, but a retry by host is susccessful. Broadcast packages every 5 seconds, and unicast data every 20 seconds. Data length is less than 200 bytes in every case.
For no apparent reason, after approx 35 hours 10 mins module no longer transmited any data. Reception was unaffected. Only a hardware reset restarted transmit communications.
Although not using CTS, CTS line was de-asserted.
Interestingly, 35.4 hours is about 131072 seconds (2^17).
Would have expected, that if API packet was corrupt or sent while CTS was de-asserted, packet would be ignored and CTS would return asserted after timeout.