Cant communicate between devices after sleep

Hi all.
I’ve got 2 digi868 modules communicating (p2p i suppose) , using the usart , just rx/tx in transparent mode.
If I put one of the modules to sleep for 30 seconds , but the other device continues to transmit , when the one device wakes up again , I can’t re-establish comms between the 2 devices. I am putting the device to sleep using the sleep mode 1 and the sleep_request line. If no comms happen while the device is asleep , then everything seems to recover ok.
I’ve tried a hardware and software reset of the “waking” device after it wakes up, does not help.
Any ideas?
I’m new to this stuff , so I’m sure I’m doing something dumb :0)

What is the exact part number of the Xbee modules you are working with and what firmware version is installed?

May I suggest you contact Digi Technical Support by sending them an email to Make sure that when you do, don’t just say I am having an issue. Make sure you provide them everything they would need to reproduce the issue.