Default [HELP] ext SD card not working.

heya
i just got a new SD card, 32gb class 10 and i think it might be defective.

when i put it into the phone and start SD tools to test speed (mnt/extSdCard) which WORK Swith another SD
here at first it tried to scan and said "error" (again, this works with another SD) and sometimes it fails to mount and says "invalid path" (same path)

not sure waht to do
i put it in my laptop (which was also problematic at first) and format it to exFAT 32 unit size but still, no go..

what am i doing wrong?

EDIT:
i now ran format via the s4 itself, it ran the test once, got a 2.4 write speed and 8.9 read, isnt that super slow for class 10? also after first test it fails to run another