I put a Sandisk 128GB card in my S7E at the time of purchase which was the day of the S7E release. I find that often the card isn't recognised by the phone and photos are saved to internal memory and it takes lots of reboots or button sequence pressing to get it to show up and then the photos on it. If I do the regular software update or restart the phone it takes loads of attempts for the card to show - annoying !!
Doing a bit of research seems this is fairly common, is it a phone issue or a Sandisk memory card issue?
Different comments on the internet say you should use a Samsung memory card and then you don't have any problems. Is this true or just a ploy to get you to buy the Samsung card as it's a Samsung phone?
The Sandisk card came from Argos, I don't know about returning it if it's the card being the problem.
Any thoughts on the Sandisk vs Samsumg card?
Could be the card. Not same phone but Moto x style some time back did same thing. In end tried a new card and no more problems. Used to be there one minute and then gone the next. Sometimes took a couple of reboots for system to see it again. Didn't last for long. New card sorted it. Both old and new cards were SanDisk but new one was faster. The replacement card is working fine in my current S8.