Zwave controller suddenly offline

Hey there,
I had quite a stable environment. All was working fine until I was forced to move to the snapshot releases due to some bugs that were already solved in the snapshots. Since then, every now and then my zwave devices cant be controlled any longer. Everything is working fine, except zwave.

When looking at it in more detail, HABmin sais, that the controller is offline (Aeon z-stick, the older one). When running OH2 in debug, the log doesnt say anything obvious.

 2017-05-20 22:14:45.466 [INFO ] [ing.zwave.handler.ZWaveSerialHandler] - Connecting to serial port '/dev/ttyUSB0'
 2017-05-20 22:14:45.656 [INFO ] [ing.zwave.handler.ZWaveSerialHandler] - Serial port is initialized
 2017-05-20 22:14:45.665 [INFO ] [mmandclass.ZWaveSecurityCommandClass] - Update networkKey
 2017-05-20 22:14:45.706 [INFO ] [ve.internal.protocol.ZWaveController] - Starting ZWave controller
 2017-05-20 22:14:45.707 [INFO ] [ve.internal.protocol.ZWaveController] - ZWave timeout is set to 5000ms. Soft reset is false.

OS logs (messages, syslog, dmesg, etc) dont reveal any obvious. Restarting openhab does not work. Re-plugging the Aeon z-wave stick does not help.

Only rebooting the whole system gets me going again so that the zwave USB stick is recognized as active again. Today happened the second time since last reboot 9 days ago. Seems to be a rare case.

I’m a bit puzzled on how to troubleshoot further. Anyone an idea?
The zwave binding is up and running all the time.

openhab> bundle:list | grep -i zwav
232 | Active   |  80 |     | ZWave Binding

Since its working after reboot, I can exclude any Hardware issues, config changes, permission issues for the serial port, etc. Anything I forgot to loog at`?
Any tips to check are welcome.
Thanks much.

Someone an idea? Any info missing to suggest something? It did not happen again till now, but the timeframe between the last two occurrences was 9 days.