I have had some issues recently with getting LTE (4G) connectivity on the Vodafone Australia Network using CyanogenMod 11 on multiple devices (http://forum.cyanogenmod.org/topic/92919-no-4g-signal-on-vodafone-au/). Turns out that it was an APN issue after all.
The APN provisioned by default when the Voda SIM card is inserted (vfinternet.au) does not work for the LTE Data Network. It works with GPRS & WCDMA, but fails to connect when the phone is set to prefer LTE (4G) Networks and they are actually available. It means that the handset will loose mobile data connectivity altogether. There are various APN Settings floating around on the interwebs, but any I tried previously did not fix the issue.
Ater needing to call Vodafone support for another device (on GPE Stock Android) that was experiencing the same issue I got given these APN Settings:
Settings –> Mobile Networks –> Access Point Names
APN Name: Vodafone AU
APN URI: live.vodafone.com
Leave all other settings at default (for MMS settings see the link to VF Support below).
I have tested this for 2 days and works beautifully. The correct APN settings can be found here: http://support.vodafone.com.au/articles/FAQ/APN-Settings