I bought mine from banggood in Feb. The sd card did not give any problems until last week. Now both android and win10 partitions cannot detect the sdcard. I am using mirek V3 for android and win10 sd drivers have been down graded to unsigned win8 versions.
Most likely a hardware issue with the sdcard slot.
There is no more support from mirek or spzjulien for the android partition.
Best to stay away from this teclast brand as, like many have stated, you will get no support or fix from Teclast.