This is most likely because in the RA there is a lifetime flag. Then when you boot again the RA has expired. As such it is working correctly for this part. Check the configured lifetime of the RA on your RA server and make it longer if needed. I've over the last years never had an issue with that though and I hibernate daily. One can even hibernate SSH sessions and they are still alive when waking up the laptop the next day (catch: no traffic should be generated from the server). Also, are you talking about the RA+EUI64 address or the privacy ones? Now that is really odd. Thus the question really is: what kind of network card is it? And which driver. Maybe, when the driver gets powered off the driver actually signals removal, which would indeed cause what you are describing and would indeed be avoided by toggling that flag.