Skip join if already joined

I have a CubeCell AB02A with the example Lorawan sketch (git version). I connect to a public gateway (500 meters away).

After disconnecting the node for a few hours, I noticed the joining goes relatively well, but when I reboot the node the joining process can last 10-15 minutes. Is there a way to skip the joining process if already joined?

If not, I see a lot of Rx Timeouts during the joining process. Is there a way to tweak the setting for a faster joining process?

The region is Europe868.

I switched Net_Reservation to ON