The problem is with "Settings > More settings > Mobile networks > network mode".
if you put to auto, it will switch the network when you making or receiving a call which disable you from any internet connection.

technically, internet using WCDMA while some place with weak signal might switch to GSM.
For me i put WCDMA only since i use internet more.

note sure about this, i am new to android and note2 technically.

perhaps other big brother here can help you on this.

as far as i concern, it seems to be the problem with the signal and carrier (maxis) that i am using.
my case, if connected to 3G or HSPDA, the internet is fine but it will not work if connected to EDGE.
You should see the icon H, H+, 3G then E on top of your phone panel.

i faced this on d 2nd weeks of using note2 (maxis also). on the 4th week, i realize by using CDMA gave me both calls function and data function work flawlessly. hence i nvr put it on auto again. only go to GSM when the area does not gave me good signal.

yet, i still can't brain y this happen

I think I asked this before but can't recall.
Due to DiGi's bad connectivity in my office.

1) Set to WCDMA only. It manages to retain H and 3G all the time.
2) Set to auto mode. It changes to EDGE sometimes and jumps back to H.

So which one is more battery effective?