SD card issues on Android Lollipop (Galaxy Tab A)

[gabrielarangel]

So I bought a microSD card (SanDisk, 32Gb) for my Galaxy Tab A (running Android 5.0.2), and I've been having a LOT of issues.
I saw many people having permission issues, but it doesn't seem to be the problem in my case.
First I noticed that, while coppying some mp4 files from my internal memory to SD card, they just stopped working. They were playing normally, but some of them got corrupted on the transfer. I tried coppying the files both directly through the tablet and through the computer, but I got too many corrupted files on both cases.
I also transfered some cbr (comics) files, and, whenever I try to transfer various files at once, they also get corrupted. It seems a bit better when I transfer one at a time, but then sometimes it also happens (there doesn't seem to be any particular reason, but sometimes it will happen repeatedly for the same file, while sometimes it can be fixed...)
Since SanDisk is a pretty standart brand for pendrives and SD cards, I don't think my card is the problem...
Is there an app or a method to transfer files that might minimize this problem? Have any of you had similar issues with SD cards?

 

[gabrielarangel]

Additionally, it now deleted a whole folder on itself?!!
I had a "Comics" folder, and suddenly it's empty...
Could some of the inbuilt cleaner apps like Smart Manager be doing this, because of the cbr/extension not being natively recognized?

 

[Habibie]

Since SanDisk is a pretty standart brand for pendrives and SD cards, I don't think my card is the problem...

Whenever I bought any USB memory card, I always test its real capacity using F3 on any of my Linux computers. If it fails the test, I will take it back to the store to exchange and/or get a full refund. This includes some SanDisk microSD cards, too.