FYI - I had exact same issue, running KitKat. Phone had intermittent connection in Germany and Switzerland. Powering phone off and on would *sometimes* give me connection, but only temporarily. My colleague had her iPhone (also an AT&T device) and experience no connection issues.
AT&T did reverse the international roaming bill for me, since I had such poor connectivity, but I'd rather have the phone work, then get reimbursed, since I really need the international service.