In my case flux was guilty for sure. Believe me, I spent loooong days chasing weird problems. Cache issue was only one of many other.Cleaning board fixed all issues and not only on that one board.It's Weller flux. It has pretty low resistance and it'...

Just for the record, I know what was the reason of the super strange behavior.It was flux. The PCB wasn't super cleaned after soldering and it caused super strange behavior.The microcontroller was behaving really odd and not only the microcontroller....

Hmm, I have no idea what's going on but today it works fine :\ I didn't have to do any change, just powered up and works like a charm.Super strange.

Thanks so much. I'll check this out today and let you know if it worked.