I've found that many OTA updates cause weird issues if you don't reset afterwards, especially Samsungs. What did you do to make it go into a bootloop the other day? Is it all wifi networks that are having issues or just at home? Have you tried forgetting the network and relogging back into it and / or resetting the modem and the router if it is only at home? It doesn't matter if every other device is working, resets can often help if you have narrowed it down to just 1 network. As far as the 3G, it's hard to say. The modem/baseband also updated and not every version works best in every region. It's possible you might see if there is another version of 4.1.2 that would have a different modem to flash.
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