A few weeks ago I received a couple of Samsung Galaxy Tab A SM-T550 brand new from Amazon.es to give them to my sons.
I already have a Galaxy Tab Pro 10.1" and used to watch, while traveling, a collection of MKV files from 1 to 10 gb size stored in a bunch of Samsung Evo's 64 Gb Micro SD's , to do so I have a OTG adapter to read the Micro SD's trough OTG micro USB.
Those cards are formatted in ExFAT due to the limitations of FAT32 for large files.
They work flawlessly in the Tab Pro (Stock 4.4.2) with MXPlayer and the proper codecs (also the AC3-DTS custom codec from XDA).
So I tried to configure my two Tab A to do the same, something that caught my attention was their behavior just out the box, one of them worked as expected with no problem but the other one refuses to read the Micro SD's and tells me to format the device because it's unreadable, I tried to use ES File Explorer Pro and when I try to access the USB it tells me that the program is only compatible with FAT32 and ExFAT, that means that it can see or access the Micro SD formatted in ExFAT.
After resetting to factory defaults a couple of times I keep looking for a reason for the different behavior of both identical tablets, except for the color.
Checked with the internal Micro SD slot and it worked with no problem.
At that time I realize what was the difference between both devices, while unpacking, one of my sons that already has an old tablet, put his Micro SD card with some content inside the tablet so we started doing some tests and realized that if you left the internal bay empty the OTG was used as expected, place the card inside the bay and the problems appear.
One of the S7's was replaced at the shop tree times because, when we show them the problem, the vendor tried to use the aforementioned cards with their showroom test units and, because those units are there to show the device to customers, usually they don't have SD cars in the internal bay, as a result their S7 works fine and mine doesn't so they gave me an other and so... tree times
I tried with a bunch of OTG adapters Micro SD cards and Pen Drives with same result...

We try to reproduce the issue with every Samsung device in the house:
Two S5 (Stock Kit Kat) updated to a Lollipop and then to Android 6.
Two tablets Galaxy Tab A with stock Marshmallow.
One A5 2016 (Stock Lollipop) updated to Android 6.
One Galaxy Tab Pro with stock 4.4.2
Two S7 (SM-G930F) with stock Marshmallow.
One S7 (SM-G935F) with stock Marshmallow.
My conclusion is that every device that came with Android 6 from the factory experienced the same behavior may be something similar occurs in other brands.
I want to show this problem to the community to find if other people can reproduce the same issue.


See More: Samsung Galaxy Tab A SM-T550 and OTG