Just want to guide you to this thread:
Noticed that a reload or a full reboot is also being discussed. Back when I had about 70 devices, I also had significant success probability in secure class key exchange right after a reboot.
To configure the device, a key exchange is still required and I remember having to do a luup reload while the vera is waiting to exchange key and manually waking up the device. I will provice @edward with some more advanced logs. I have no problem reproducing this issue as I have 0% chance of secure inclusion from my vera these days.