[Samsung Galaxy S22 Ultra] lestatab:
Long story short, changing the csc to TMB (or the csc of your country) and disabling cidmanager is enough (Update4).

Yeah, yeah, I know. It's a well-documented and apparently unsolvable problem, but after trying several options that I read about, I solved it. If someone can check, it would be great.

My phone is an SM-S908U1, second hand, XAA with Android 13.

From the beginning, it lost signal. However, when I was near a tower, it activated LTE and worked correctly. It never switched to 3G in low signal areas, and if I selected 3G in the preferred network, I had no internet or it was intermittent without being able to use it. I tried a factory reset, reset network, manually installed APN, changed preferred network in all options, safe mode, hard reset, clear cache, but nothing worked.

First, I thought, let's update the ROM. For XAA, the latest is Android 14 build 20231207191201. No problem, I installed it with Odin (with USB debugging enabled), and everything was nice, all fluid but weak signal, reaching -120/-130, whereas my old phone had -80/-90. Image signal strength same sim phone above vs s22 ultra.jpg

Well, let's see the bands. I downloaded the SamFw Tool and enabled the Verizon Secret Code. All bands selected. I took advantage and activated all 5G bands, rebooted, tried a physical SIM of Telcel, Movistar, AT&T, and nothing. Weak LTE signal and does not automatically switch to 3G.

I kept reading, and some people talked about changing something physical (board). At this point, I was thinking about returning the phone. I read about CSC. With the same SamFw, I changed to FKR (because I saw that it has a more recent build of Android 14). Curiously, my phone had no SIM inserted. I rebooted, enabled USB debugging, powered off, flashed with Odin, rebooted, all okay with FKR in Software Info section (Settings - About - Software Info - Software Version Provider - FKR/FKR,FKR/XAU). I inserted the SIM, prompts reboot to Update Service Provider, reboot returns weak signal, and I have XAA again.

I had already read that someone said that you had to restore the cell, enter without SIM and without Wi-Fi, and disable updates from Connections (Connections - More settings - Keep system settings updated) and disable Updates on Reboot from Developer Options. So, I started over, changed the CSC back to FKR, flashed again, set up everything without SIM or Wi-Fi, disabled update options, and by the way, disabled the cidmanager app (just in case and from ADB). I inserted my SIM, my APN is installed, I have internet with signal -80/-90, I switch to 3G, still with internet and now no problem. When I am in low signal areas, it automatically switches to H or H+ with internet.

I guess some steps can be simplified, maybe it is not necessary to switch to FKR (I tried and it did not work, but maybe I missed to disable some of the options of the updates or the app cidmanager). But so far, the phone works without a problem.

Something curious that I have seen is that when I configured the phone all in the original way and updated the Service Provider, my logo was LTE and LTE+. Now my logo is 4G. I don't know much about it. All I did was trial and error, and luckily, I didn't damage my equipment in the process.

P.S. The Preferred Network selector does not appear, probably because the Service Provider has not been updated. I use 4GLTE Switcher - Phone Info - Launch Mode - Set Preferred Network Type. Update, thats depends of CSC Provider

Update. I just came back from a town and again the weak signal problem, I happened to disable VoLTE Calling and and it worked, it went to H/H+/4G signal.

Summary of the steps without flashing tks to @silvershadow

1) remove sim, disable wifi

2) factory reset phone

3) don't insert Sim, don't connect to wifi

4) disable keep system settings updated (connections options - more options)

5) disable updates on reboot (developer options)

6) disabled the cidmanager app from ADB

7) disable VoLTE Calling (connections options - mobile networks, maybe it appears after insert sim)

8) then insert Sim

Update2. Ok, I switched my csc to ATT and now LTE and VoLTE are working properly, the issue is the csc and that it is not changed with cidmanager?

Update3. With csc to ATT 3g (H/H+) was not working, so I switched to GCF and Preferred Network LTE only, so far the best option I have found.

Update4. I investigated my imei and it is t-mobile unlocked, I just switched the CSC to t-mobile (TMB) and it works 3G (H/H+) 4G (LTE/LTE+), it automatically switches between the two, I have internet with both modes. Too bad there is no 5G in my area.

Update5. I keep trying things, I checked samfw.com and saw that the SM-S908U model had an update a few days ago 20240131180940/S908U_ATT_S908USQS4DXAG ATT CSC so I decided to try ('T-Mobile-ATT ROM' image), I flashed it with odin and I see that it starts the T-Mobile logo (image 'T-Mobile splash'), so far it works better than the rom for S908U1, you see the images how it behaves 5G/4G/3G and 2G ('T-Mobile-network-N' images)

Update6. I continued with the problem of disconnection and no internet on 3g, so I flashed the rom 20240131180940/S908U_ATT_S908USQS4DXAG, now it starts with the ATT logo and some ATT tools for mobile networks, however, I still have the same problem of disconnections in general and slow internet or no internet on 3g. Attached a speed test while the connection was stable (speed test.jpg). I will try to replace the antenna and flex, if it doesn't work, I will sell it for parts.