FP3 mobile data connection not reliable, requires turning it off and on

[grimsa]

Summary of the problem:
After turning off WiFi or leaving the area with WiFi network, mobile data connection works only after turning mobile data off and on again.

Details
Phone: FP3+
Android version: Fairphone Android 11, latest security patch version 8901.4.A.0023.0 (but I’ve had this problem for at least a year now)
Network provider: Tele2 (Lithuania), but the problem persisted when traveling in other EU countries
Network quality: Most of the time I’m in a city with excellent signal strength/network speed, so it does not seem related to signal strength
Phone uses just one SIM
Settings:

• Mobile network → Preferred network type = Automatic (4G/3G/2G)
• Mobile network → Access Point Names = a single correct value for my provider (also tried resetting to default, which restored the same value)

Reproduction steps
I can reproduce the problem every time like this:

1. Have both WiFi and mobile data on, everything works (apps use WiFi)
2. Turn off WiFi, mobile data is still on. Internet does not work.

• The status bar at the top shows up and down triangles (indicating network activity?) on the left side of the “LTE”, but at the same time I have a small “x” at the bottom of the network strength icon. (See screenshot 1)

3. If I turn off and on mobile data, then Internet works reliably (at least in the app that is ).

Additionally, I have noticed that the phone loses mobile data connection when switching apps, for example:

1. I have a browser open with working mobile data connection, I can use multiple tabs - everything works as expected
2. I open Google Maps App, it tries connecting but times out.
3. In order to use Google Maps, I have to disable and enable mobile data. After that Google Maps app has access to the Internet.

It feels like only one app can use mobile data connection at the time, while requests from others are timing out. I’m not 100%, maybe in some cases several apps work in parallel, but I find myself having to restart mobile data quite often.

What I tried
I don’t exactly remember if the problem started after some update or from the very start.
I’ve tried waiting for maybe a year or more in case it was a regression in a software release, but security patches came and went, and the problem persisted.
I also tried restarting the phone (a number of times) with no effect.

The ask
Has anyone encountered a similar problem?
Do you have ideas how I could troubleshoot and fix it?

Thanks!

[grimsa]

The issue is still present after updating to Android 13 (build 6.A.018.0)

[AnotherElk]

@grimsa

Do you have ideas how I could troubleshoot and fix it?

In the Developer options (made visible by tapping on the Build number in Settings - About phone a few times until you are being declared a developer) there should be a switch “Mobile data always active” … perhaps toggling this into the state it is not in now might make a difference.
(If it is enabled now, disabling it might trigger mobile data being turned on successfully when leaving the Wi-Fi network. If it is disabled now, enabling it might keep a working connection in place.)

Else …

@AnotherElk

• Turn off the phone (not just a reboot, real shutdown), then turn it on again
• Reseat the SIM card while the phone is turned off (can’t hurt)
• Network reset (search the Settings for “reset” and go with “Reset Wi-Fi, mobile & Bluetooth” or similar)
• Factory reset (search the Settings for “reset”, will delete user data as well as Apps installed by the user and their data)
• OS install from scratch

Regarding OS install from scratch, the Android 13 install file wasn’t released yet … https://support.fairphone.com/hc/en-us/articles/360048050332

[grimsa]

In the Developer options (made visible by tapping on the Build number in Settings - About phone a few times until you are being declared a developer) there should be a switch “Mobile data always active” … perhaps toggling this into the state it is not in now might make a difference.

Thanks for the suggestion. I tried that with no luck just now.
“Mobile data always active” setting was off initially. I turned it on, tried restarting the phone, and then getting on mobile data (Internet worked via mobile data), turning on WiFi (internet worked via WiFi), turning off WiFi (mobile data connection shows “Connected / LTE”, but interned did not work without turning it off and on again).