S21 update to Android 12 - SIM continuously resetting

[gpaolo79]

Hello,

three days ago I have received the update to Android 12 on my Galaxy S21 5G  and, since then, the phone is almost unusable to make phone calls

Both sims reset themselves periodically, within minutes, dropping the network and any phone call in progress. 

After trying to reset the network settings, the phone has started to request the pin for the sims at each reset, so I had to disable it. Keeping one or the other sim active only isn't changing the behaviour. 

The diagnostic on the phone doesn't detect any issue even if run while the network is down. 

Does anyone incurred in the same issue or found any solution? The phone is 3 months old...

[hasham11]

Go to the apn settings and then click your currently selected apn, then go all the way down, you will see the "bearer" option. 

[gpaolo79]

Doh

Didn't know the existence of that menu

I'm still not sure though, the translation seems to be different. The only option that I can see that contains LTE is "connection" for me. I tried to change that, it was undefined, now I have set LTE. Let's see... 

[gpaolo79]

And no, just had a reset. Doesn't work for me. 

[gpaolo79 · Accepted solution]

So, after that one Samsung center refused to change the motherboard, another tried but Samsung cancelled the order of spares and now I don't have time to wait any more, I decided to downgrade back to A11 and it seems to be once again stable.

From the next version the bootloader should be different and not allow the downgrade to A11 any more, so if you have these problems, I would suggest to downgrade now, don't enter wifi during setup, go straight to software update and disable them before doing anything else.

For me, A12 can wait. I am not impressed with Samsung, one month of time wasted with a non-usable phone, and at the end I had to "solve" it by myself reverting back to the previous version of Android. Not good at all for a phone of this price.

[hasham11]

Downgrading to android 11 means you lose all your data, apps, setting etc.?

Also, is it easy to downgrade or you have to reflash the software manually through odin? 

[gpaolo79]

Downgrade means losing everything, but with smart switch you restore all apps and settings quickly.
It has to be done manually with odin. It's not difficult, just a few clicks, but you need to view a few tutorials to get a complete idea of what to do and expect.
For me, it wasn't really a choice...

[hasham11]

Oh okay. For the time being, using a single sim, I am facing no issue, trying out dual sim since last night after a new update on 28th, no resets yet. Let's see how it works going forward. 

[hasham11]

OK just had a network reset. Have to use single sim mode for it to work without any resets, Samsung pls release a fix soon. 

[christo574]

The Pixel 6 have sames issues and use almost the same SoC as the S21 Ultra. Wait for the January update...

https://www.androidpolice.com/google-pixel-6-pro-december-update-pulled/

[hasham11]

Looks like a similar issue we are facing with the S21 Ultra, Jan update will come around end of Jan, so almost a month to go by without dual sim mode. Also recently noticed network reset with single sim mode too, but it's like once or twice a day, liveable, but definitely annoying.