No, by no means. As long as the module is flashed with the newer firmware it will work nicely for all spreading factors apart from SF12. (And even that won’t be a problem first few years)
Ok, i am using SF 12. So i will change it to 11 and flash a new firmware.
Now i flashed newest firmware and changed spreading factor to 11. But the result ist unfortunately the same.
I also changed the timing for wakeup condition (break 300µs + 0x55) like in the picture. The answer from the modul is OK. 
Problem captured and solved. In a function i had send the sleep command twice.
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Make sure the mac state is idle before sending sleep. Otherwise the RN2903 hangs. I don’t know whether the RN2483 suffers from the same problem.
Im actually having similar problem - to save power on the uC im turning the UART off which causes the RX line on RN2483 to go low - Im unable to wakeup the module once I bing the line up again and send the ‘0x55’ char. Any suggestion here?
Try, before enabling the UART, set the RX pin as an input with internal pull-up enabled.