Strange network connection quality problem with dual sim

[RaoulTeeuwen]

Hello.

My employer gave me a S21 5G phone. I use it with a physical SIM in slot 1 and an eSIM. People told me they had problems contacting me on my SIM1 number. I fiddled around with settings.

If i set 'Network mode' (Settings/Connections/Mobile Networks) for the eSIM to '3G only', network quality for SIM1 shows all bars. If i toggle the Network mode of the eSIM to anything else, the quality drops significantly, probably causing, in areas with less reception like in buildings, the SIM1 to have 1 bar or worse.

Roaming, VoLTE toggling etc doesn't seem to influence this. And the behaviour is repeatable (toggle Network mode influences connection quality bars of SIM1).

Anybody have any idea? Is this a design flaw, with 2 radio modules (one for every of the dual SIMs) that influence each other, leading to lower connection quality?

[WelshPaul]

I have a physical SIM inserted to slot 1 and an eSIM activated.

SIM Network mode: LTE/3G/24 (auto connect)

eSIM Network mode: 5G/LTE/3G/24 (auto connect)

Are you sure it's not just a case of poor 4G/5G coverage? It probably shoots up to full when switching to 3G because you have good 3G coverage.

[BandOfBrothers]

Hi @RaoulTeeuwen 

I'm using a different phone model but when I do insert two sim cards I'm not experiencing the same as you.

A Samsung Experience Store or Samsung Service Centre can take a look if you wish.

[RaoulTeeuwen]

Thank you for your reply. I understand my description is not clear. I have bad reception on (physical) SIM1 when i have the eSIM set to auto switch between 2/3/4/5 G. When i force the eSIM to use 3G, the network quality of SIM1 (!) improves dramatically. When i switch the eSIM back to auto 2/3/4/5 G, the SIM1 (!) network quality drop significantly. I can demo this consistantly.

[RaoulTeeuwen]

Thank your for the reply. Good to hear. Just checking: do you also have both 1 physical sim (in slot 1) and an eSIM? Could be different from 2 physical SIMs?

[WelshPaul]

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@RaoulTeeuwen wrote:

Thank you for your reply. I understand my description is not clear. I have bad reception on (physical) SIM1 when i have the eSIM set to auto switch between 2/3/4/5 G. When i force the eSIM to use 3G, the network quality of SIM1 (!) improves dramatically. When i switch the eSIM back to auto 2/3/4/5 G, the SIM1 (!) network quality drop significantly. I can demo this consistantly.

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I just checked and my O2 SIM in slot 1 is using the 3G network and not 4G even though its set to use LTE/3G/24 (auto connect). O2 coverage map shows 4G as being the same as 3G in my area. 🤔

EDIT: OK something weird is going on... If I change the eSIM to use a network mode such as 3G/24 (auto connect) SIM 1 switches to EDGE and no longer uses UTMS. It doesn't appear to connect to 4G at all! So I think you have stumbled upon an issue here!

EDIT 2: I just disabled my eSIM and SIM 1 now connects to 4G. With eSIM enabled, SIM 1 will only connect to 3G network and not 4G. 😲

EDIT 3: SIM 1 has now fallen back to 3G. Maybe it's just down to poor coverage on O2? I will do some testing throughout the day and report back!

[BandOfBrothers]

I use two physical sims.

[RaoulTeeuwen]

If anyone knows how to maybe have someone from Samsung look at this, i would love to hear. I really think, at least in my phone, with my combination (physical SIM and eSIM), something is wrong.

[cheflaszlo]

i have same issue. not just poor coverage but phone goes nuts, not entering 5G tower easily, lost signal, hard recovering.  very bad. i need to know how can be fixed

[manikrishchinna]

Hi,

I am also facing the same problem with Galaxy S21 in India. I if use dual sim either physical or eSIM, I am facing data speed issues. The signal strength showing good and the data connectivity also showing but data speed is poor. Same network, same location if I remove one sim, it works perfect.