Hi, Jef.
I've found the similar issue on my samsung tablet SM-T110.
I've found that if I copy files from my computer to the tablet, into the folder "Dowloads" I can then find them from tablet and to use.
So, the communication works in one direction.
But I wasn't able to read any tablet's files, even that ones I copied before, from my PC.
I've turned on the USB debugging, but I was able only to switch between two options: connect my tablet as "Media device"(MTP) or as "Camera".
In "Camera" mode I was able to read from tablet the pictures that I made by the tablet's camera. But the other my files are not visible even from the same folder.
So, I'm still very curious, how to read ANY kind of files from my Android device.
Alex.