I keep saying, look for a UHS 1 microSD card.
That is, look for a card that puts the UHS rating before the Class rating. I'm using a microSD card that was labeled "USH 1/Class 6" and it works better than a card that was labeled "Class 10/UHS 1". Even though, Class 10 has the same same through-put as UHS I.
I've also recently found out that there are different host controller chips for SD cards. A host controller chip that was made for "Class" rated cards is different than a host controller chip made for "UHS" rated cards. Neither controller chip handles the other rated SD cards very well, but are compatible with each other. I believe that Microsoft or Nokia spec'ed out that WP uses UHS host controller chips, which is newer and is capable of higher speeds and storage space with UHS II specifications.
Which is why I think most people are having issues with microSD cards. Primary "Class" rated cards are EVERYWHERE, where-as primary "UHS" rated cards are a bit harder to find. But they are out there.