I am also having the same issue with my S8+. I got this phone few month ago and until now, my SD card slot was empty. I just entered my old 32GB SD card from my old Android phone and my S8+ won't recognize it. Only way I can make it work is while the power is on, use a pin and eject the SIM/SD slot. The screen will say close the slot. When I did it, the phone will recognize the SD and working fine. But every time I restart the unit or turned it OFF/ON, it will stop recognizing.
I have the problem with the SD card not reading picture, I'll take a few and they will be there but take a few more and they won't be! Really annoying because I take and post a lot of pictures!
I tried everything mentioned on this thread, with no luck. Then read somewhere else about disabling the Google Play Store App. I did it, and it has been a few days now with no further problems.
I had to download an app, so enabled it, and had immediately problems again. Disabled it again, and all ok now.
Hope it works for you, try it and let us know?
Great! Glad it also worked for you. My sd card did unmount one more time a few days ago, but it seems to be working fine since then.
Just find it VERY Hard to believe that there was a Samsung support person on this forum, that referred the issue to the technical department a long time ago. But he has gone completely quiet with no further interaction with us, the users with VALID complaints on the product, that can surely not just be flatly ignored??!!
I just had the same issue! I've only had the S8 for a few weeks and I am using the sd card from my S5. 64Gb samsung card. I tried shutting down and unmounting and that didn't seem to work. I then went in and updated my PRL and profile and rechecked for any new software updates (I was up to date). Not sure if any of these things helped but I have my sd card showing again. Hopefully the problem doesn't come back.
*update* Ok. Didn't work. SD card is "gone" again. I tried everything I did last time and I disabled google play as suggested above. Nothing worked. It's not coming back
My SD card has been good for a while now. I made sure it was in the tray properly, pushing on it until I thought I broke it! I also have had my phone in mid power save mode which prevents apps from starting in the back ground. So far so good! No ejects since. Not sure which of these things helped. Possibly both. I will put it back in regular power mode and see if it ejects again. That would tell me that it is definitely an app running that is causing it. I saw a few people mention that the SD card ejects when they haven't been using the phone for a bit. I noticed the same. I will update again soon.
*update* Day #3 since reseating my SD card and all is still well. I took it out of power saving mode and it is still doing fine....fingers crossed