We'd like you to try Safe Mode, @colinspencer. To activate this, restart your phone but whilst it's powering back up, keep the 'Volume Down' button held until you reach the home screen. If done correctly, Safe Mode will be displayed in the bottom left corner. Let us know if your SIM card is recognised during this.
I have the same issue and only this morning the 2nd sim is still working in the camp and when I go to the office the sim is not recognize at all and indicates NO SIM. I tried to swap the sim but still the same, I asked my co-office if he has signal with the same provider of my 2nd sim and he has. is there any solution on this one and please share to the community. Thanks...:manhappy::manhappy::manhappy:
I dont think Samsung has recognized this as a problem. I had Sprint give me a new sim card and haven't had any issues since. My thought process was maybe it was just an older sim card and while it worked most of the time, the age caused it to not want to play well w my phone. I could go 3-4 months no issue, then it would stop recognizing it 4-5 times in 2 days! It was frustrating!! My suggestion is a brand new sim card. Good Luck!
@TaminatorThank you so much! This is the only thing that helped me. And I even factory reset and that didn't work.
This may not be a fix for everyone but this issue started happening to my husband's s8 back in October 2017. It got more frequent over time. I search all over the internet but none of the fixes worked until we came across a poster that said she changed her mobile network band to GSM. It was under an "AT&T" forum. My husband has an unlocked s8 that is used on AT&T's network. We did the following (and it has worked so far). You can find youtube videos on how to change the mobile network if you need visuals:
1. dial this number (like you were making a phone call): *#*#4636#*#*
2. You will then see a "secret" menu and can get to your mobile network band through selecting "phone info". You will need to scroll through slowly to find the line to select mobile band.
3. If you are on AT&T or T-Mobile, you need to select a GSM band. We chose "GSM auto (prl)".
4. If you are on Verizon or Sprint, select CDMA.
I don't know who runs on LTE, but that was what my husband's phone was set at and it was NOT working for At&T. It seems to be running even faster and he hasn't had the warning since but we changed it last night and it's not been proven 100% yet. I'll try to update with anything new. PS - I am no techie or expert so if I'm totally off on this, sorry.
You probably have it figured out by now but I was having the same problem so I was about to take out the sim card with a toothpick in the sim card hole on the top left of my phone but it wouldnt pop out so I stopped and just blew really hard into the sim card release hole. This somehow fixed the problem so, hope this helps!