Error Code 125012S

What worked for you ? 

Open your EA app on PC, click the the lines in the top left, hover over "help" then click "App Recovery".

Click "clear cache"

The app will restart l, launch Battlefield and play.

Works for me every time, but occasionally need to log out of app, log in, then clear cache.

I found a workaround that is 97%+ successful. You must first load into a Solo/Co-op match BY YOURSELF for your first match of the day. Once you're in the match and moving around, your friends must join your game in progress. You must complete the match (if you have the bots on easy mode you can blitz through it) and then bring everyone with you back to the main menu once the rewards screen shows. From there, you can queue into normal multiplayer matches. However, this is not intended to be (and should not have to be) a permanent or guaranteed fix. If you get that error code, it's game over for the rest of the day or until around 2000 U.S. Mountain Time (inconsistently). For some reason, I've had better luck overcoming that error code once I get it after the aforementioned time in the evenings. I believe the source of the error code stems from trying to load/combine your player data with your friends' data when attempting to join their game, even if you try to join their match in progress. Good luck.

I found a workaround that is 97%+ successful. You must first load into a Solo/Co-op match BY YOURSELF for your first match of the day. Once you're in the match and moving around, your friends must join your game in progress. You must complete the match (if you have the bots on easy mode you can blitz through it) and then bring everyone with you back to the main menu once the rewards screen shows. From there, you can queue into normal multiplayer matches. However, this is not intended to be (and should not have to be) a permanent or guaranteed fix. If you get that error code, it's game over for the rest of the day or until around 2000 U.S. Mountain Time (inconsistently). For some reason, I've had better luck overcoming that error code once I get it after the aforementioned time in the evenings. I believe the source of the error code stems from trying to load/combine your player data with your friends' data when attempting to join their game, even if you try to join their match in progress. Good luck everyone.

Nope! In Season 7.  I play only on Xbox and downloaded EA app to my PC just to accept my friends friends request. And after that this damn error showed up. 

Please Find a good damn fix to this already. BF2042 is a really good game and I finally can play with some friends and this happens.... 

Any fixes for this issue yet?

unlink ur xbox account from your EA account.
Also using a VPN can help bypass this error or changing your routers MAC address can sometimes generate a new IP from your provider.
I play on 3 platforms and its a nightmare, then you get on and the nightmare becomes a living nightmare cause the servers suck.
Then they buffed console players to the point it's 1 frame death thru walls every time from them.
https://i.redd.it/can-someone-explain-this-v0-5fhwyekjqctb1.png?s=22b8571fad90bcc1f5a63b98386d16840842a17f