Disable write-protection on Micro SD

Dust out your adapter. The sensor inside of it may be dirty and not recognizing the position of the switch.

I would also try another SD<->MicroSD adapter.

If you still experience problems, try putting a questionable SD card inside of a phone. I'd say if you get 2 or 3 cards that work fine in a phone, you should replace your USB card reader, see if maybe there is an issue with your USB connection, or use Linux to perform the task if possible which tends to behave a lot better regarding removal/insertion of USB devices, disks, and volumes than Windows (OSX also likely behaves a lot better).

If you find that the MicroSD cards are actually write protected (which should not be possible - the host/card reader is responsible for implementing the write protection and switch sensing, not the microcontroller in the card), I'd keep the bad ones and demand a refund.

I have been fighting this issue for weeks and here is the way I found to fix. When MicroSD shows that it is write protected or locked. You have ensured if you are using an adapter the lock switch is in the correct position.

Download SD Formatter v4.0 from SD association website. Under Format Option Click to Format Type Full (Overwrite) Start this process. Please note you will lose all information on the card at this time.

After for me I still had to format the SD card in windows for it to recognize. Please allow a full format in windows and you should be good to go. I have not found anything else or any other website to be of any use when it comes to the microSD acting in this way.

SanDisk did issue me an RMA to return the unit. so if this does not fix the problem I would recommend contacting the MFR for a replacement.