Thats not normal. Boot into stock revocery and wipe the phone or take it back. Mine never did that. Only problems were a few apps crashing from rooting it and playing with settings. Stock wise no call drop outs or dcing data unless its my provider optus being crappy.
The phone for me is running as stable as a pc haha so good!
Sent from my SM-G900I using XDA Premium 4 mobile app
S5 running xtrestolite and ktoons kernal + luigis profile.