I bought SAMSUNG PRO Plus + Reader 256GB microSDXC (mb-md256kb/am) few months ago. The read speed is normal (160MB/s), but write speed is extremely slow (12MB/s) for large file. I try different format, different card reader, on different machines.
How can I fix this? I tried to request warranty service. It kept asking me to register the device, which is not possible. Card only has 12-digit serial number. Is there a simple replacement service? How can I request it? I did buy the card on Samsung official website.