the_o2 , Nov 25, 2020 : Do as mentioned here Meanwhile report this bug here as well https://forums.oneplus.com/feedback
Shailender Sharma , Nov 25, 2020 : Check this thread out - https://qwikfone.medium.com/how-to-fix-no-sim-card-detected-error-4d7c4421c7ac
Sathya8802 , via OnePlus Nord , Nov 25, 2020 : What I should do to come out of this problem.Please tell me sir.
khan1992 , via OnePlus Nord , Nov 25, 2020 : Even I'm facing issue in my sim 1 slot there's exclamation sign over the Network due to this issue internet is not working
Sathya8802 , via OnePlus Nord , Nov 25, 2020 : Brother follow this process. In the very beginning both of my sim was working fine then one was playing COD and I activated fnatic mode which results in deactivating the second sim. This will always happen. Then I just simple closed the game after playing and since then the issue begane and there was no option to switch back the sim 2. But what I did to fix the same was, I started my COD and once the gaming mode gets activated, I scroll down the system icon tray and clicked on exit on the gaming mode and it just simply activated my second sim. So the final verdict is before closing the game you need to exit the gaming mode from the drop down. And that's it. Hope it helps, feel free to revert back. Cheers🥂