Windows Phone 8.1 roaming issues

This year I bought a Nokia Lumia 620 in spite of the fact that everybody told me that is not the best idea. The thing is that they are wrong, the phone actually works perfectly for the price and Windows Phone 8.1 is not a bad OS. In fact I still think is better than Android but beware dear users because it is not stable yet. I had some minor problems with it but until now I was always saying is OK, at least my phone does not have lags and does not restart during a conversation.
Well, I was really disappointed when I was in vacation in Greece and my phone was constantly freezing in roaming and during the freeze the battery was drained in 2 hours, so totally unusable. I wasn't able to fix the issue but I know I didn't had the automatic network selection option set. And the freeze usually happened when I lost signal but anyway that's not an excuse for this terrible bug, very disappointing.
EDIT
I found the issue with this phone. It wasn't the Windows Phone OS but a hardware issue. The problem was with the heat. The phone is actually too sensitive to high temperatures.