I jammed blu-tack into my SD lock switch. Those things are pointless anyway, the SD card doesn't write lock itself, it just asks the reader to pretty please not write to it.Did you tried tape trick for SD card lock latch?
I have this issue sometime with multiple sd card adapter then I found the lock latch not too loose but it easy to change the position when put into the wii u card reader slot. Used thin tape to prevent it sliding then I never got the issue again.