Continuous reboot after landing in foreign country

Hello,

I am experiencing a really strange behaviour on my 9810.
I travel frequently between France and Germany, I have 2 SIM cards. The original SIM was french and the device worked OK in France.
I then when to Germany, change the SIM card and it worked OK.
Now when I get back to France, upon landing the device gets stuck in a continuous reboot loop. I tried:
- battery pull
- Battery pull + french SIM card.
- battery pull + leave the german SIM card
- battery pull + no SIM card

As soon as I land back in Germany the device works perfectly fine again.

As I got back to Germany I flashed the firmware to the latest I could find and when I travelled again the issue reoccured.

Frankly it seems a bit magic to me that the device would reboot even without any SIM card.
Any ideas?

Thanks you.

BTW it seems that leaving the device in 2G just does not change anything.