On the risk of going against the rules, I am the same Meizu Blue.
@Irfan Latif My SD card's system was FAT32; reformatted it to exFat, now the phone won't read it (still working fine with desktop). Android version is apparently based on Nougat, OS is Flyme 7.1 Global. Phone file explorer is built-in/default; desktop is Windows Explorer.
UPDATE: The SD card worked fine in another phone (Realmi2Pro, with a custom OS). For now, we suspect it's the problem with Flyme 7 OS.
FINAL UPDATE: The micro SD works after I downgraded the Flyme OS to the latest 6 series. I guess it's an OS problem after all.