Dual sim is broken?

[Kaare]

I have two sim cards, but since getting the second sim card, the phone keeps acting weird.

To be clear: when I remove the new sim card, and make sure all settings point to sim 1, my phone goes back to working like normal.
However, when I add a second sim, the first stops working. At first it seemed like the problem was in managing which card had 4G, however, now it’s at the point where I can completely disable the second card, make sure the first is preferred for everything, and still that card won’t work as normal. I have to take out the other card.
It’s an intermittent problem - a few days ago things seemed to work, with me even having data on the second card, but that has now stopped working completely. I was in the shop where I bought the sim when I first experienced problems, but there it turned out that the sim was only faulty when placed in my phone. It’s of course possible that the sim itself has now broken, but I am suspecting that it’s the phone.
Does anyone have any experience with this?

[Friek]

Hi,
on my phone the two SIMs are working fine. It might be a problem with the type of SIM card you have.
Try this or this wiki

[Kaare]

well, both sim cards are new, and it’s not the location-resetting bug (I had that one too). …

[Patrick1]

Dual-Sim generally works fine. It probably is your sim card combination or a misconfiguration. You said it once seem to work a few days ago.
So I cannot believe the phone itself is broken.
Most important to know is that when using two sim cards at least one of them need to be set up to using the 2G network only.
But it is free to assign it to any slot or card.

I am using a sim for calling from “Blau” provider and a data/call sim from 1&1. All works fine here.