Xbee with Arduino only receiving data from one Xbee

Hi all!

For a project I’m working on I’m using 3 Xbees (Series 2). 2 are connected via Arduino (Wireless SD shield) to a couple of sensors and sending serial data via Xbee. The third is connected to a Controllino Maxi with a Sparkfun Xbee Explorer.
I can send and receive data perfectly fine, the problem is that I can’t receive data from both Xbees on the Controllino. When I have the receiving Xbee hooked up to my PC and reading with XCTU I can clearly see both streams.

The library using with the controllino: https://pastebin.com/9rDDtwhf
The code for the controllino: https://pastebin.com/0SV1MtgR

Try creating a buffer in which to read the incoming data from the DO line of the XBee. Or try using hardware flow control.