Question [Q] About OTG performance - possible reasons

Never before had I a chance to use the so called " On The Go " function . I perceived the most advantage of this function during the travel of last week through my friend.In and out of devices ,very convenient. So when I came back, I ordered at once the same item with him , a SD card reader adapter with OTG. ( I bought it after I read the instruction details and affirm its compatibility with my tablet and phone.)
Firstly I use it with my Samsung Galaxy Tab. The item goes well and I can reach my data quickly and completely. Then I plug it into Nexus 5 with the same Micro SD card. My phone sense this "invader" very slowly. Something is wrong with my data. The data on the card are not shown completely. A part of the data disappear.
I have no experience like this. Any possible reasons why this strange phenomenon happened. Any suggestion prefereed !!