I have one at work (not Transcend) that had a similar issue with SD cards. I opened it up and found that the SD slot has a metal cover over the circuit board and is soldered on at a few points. One of the points had a broken solder joint (cold solder joint?) and after I soldered that leg back on, it worked fine afterwards.
Pain in the ass, and it might be easier just to get a new one to be honest though but that depends on how much your time is worth.
I just bought a Kingston drive for personal use. At $12, it cost about twice what the other ones cost, but a lot better compared to the old one I had. It can read 20 MBps while the old one did only 5MBps.