How to properly replace a broken ZigBee coordinator?

ZigBee - Bindings | openHAB and Zigbee 3.0 USB Dongle Plus | ZBDongle-E | ITEAD STUDIO OFFICIAL contradict each other re HW flow control.

Any proof (log files etc.) that communication problems are the root cause? Any battery operated Zigbee devices involved?

My setup (two separate Zigbee networks bridged by openHAB):