Help analysing 4G connection problem

I have both an XA2 and a Xperia 10 III running Sailfish X. Both can’t connect to 4G with my main provider.

On my XA2 I can sometimes get a connection, but usually I loose it after a reboot or just like that after a couple of days. Getting connected again seems a random affair and may sometimes not happen for days, sometimes it gets reconnected after a couple of hours. It’s really annoying me. I can get a 4G connection (in either simcard slot) with my 2nd provider. I also tried removing the 2nd sim and swapping the sim cards, but nothing helped.

I had hoped that it was a phone related issue, but my Xperia 10 III also has this problem. Before flashing the phone yesterday, I had no problems connecting to 5G. So I’ve come to the conclusion that it’s not the phone which is the problem.

The reason for not using the 2nd sim for 4G is that this is a prepaid sim which I mainly use for receiving calls. I would like to have internet on the go using my subscription service.

I have no idea how to progress from here. How do I find out what is causing the problem and fix this?

Does the SIM card work fine in other phones?

I’d suggest replacing the SIM card.

Edit: you mention 5G, I assume you meant 4G in that spot, too?

Hey, thanks for helping out.

Yes, the sims work in my Fairphone 2, which I still have as a backup. (actually I considered going back to android by buying a FP4 with iodé, but I decided to stick with SFOS and buy the Xperia 10 III)

When testing before flashing the Xperia 10 III, it automatically switched to 5G, so I assumed that 4G would work on the Xperia 10 III.

The sim card from my primary provider is a plan which has two sim cards, so I can use multiple phones. I do not use both of them concurrently, so there should not be a network conflict because of that.

The Fairphone works in 4G, so that’s good.

Is your country and operator already listes in the VoLTE test results? VoLTE provider support

So does the phones stay on 3G always? Or just during calls? The phones should idle in 4G network no matter what, as long as you gave “prefer 4G” set in the settings. VoLTE requires flipping the switch on for both devices.

Sometimes the initial 4G requires aome time, so juat leaving the phone be overnight could help… Or flipping the flight mode on and off.

Do you have mobile data enabled and functional? That shouldn’t be related, but it’s in the same ballpark anyway…

One more obvious thing is coverage for 4G.

Neither phone even does 3G, it’s just 2G. (Both XA2 and Xperia 10 III) The problem has been occurring since around april on the XA2.

Coverage for 4G should not be an issue. It works for my FP2 and worked for my Xperia 10 III before flashing.

My provider has been tested by others in the VoLTE topic. It should be okay.

I’m looking for ways to see what is causing the problems. Are there any logs I can inspect? I’m not very familiar with diagnosing this kind of problem.

Update: I went to a local shop of my provider in town. I had the sim cards swapped. They still don’t work on Sailfish. I had a momentary connection after swapping internet to the 2nd provider and then back again. But once I did a reboot to check if it would work out of the box, it didn’t come back online. I’m starting to think it’s Sailfish OS.

Also, when I have to select a network, for example when I’m on the road and I want to download something, but the connection has degraded to 2G, and I tap the first provider’s simcard, it will immediately say that it cannot connect.

Update 2: Ok, I figured it out. The people at the helpdesk were wrong. Apparently I need to enter a different APN name. Somehow the guy at the store didn’t spot this. Also weird that the automatic setting sets up the wrong APN name.