Upgraded my GT-i9305T to the latest CyanogenMod nightly, and had quite a few issues. Namely, my phone would no longer connect to 3G/4G, and the APN settings were blank. Trying to re-enter APN settings didn’t work (nothing would go into the APN list!). I tried rolling back to a previous nightly, but then the phone just kept rebooting.
The solution was to install the nightly above, and then reboot into ClockwordMod and clear the cache. After I did that and rebooted, my APN settings were normal and I connected to the data network without issues.