Dolphin 16.08.0 can copy files from Nexus 7 2013 device, but can't paste files onto it. 1. Open your home folder and copy a file 2. Try to paste it to a Nexus 7 2013 device via USB (mtp mode) The "paste" entry in the context menu is greyed-out. Gmtp, a third-party application, sends files to the tablet via USB without any problems. KDE Connect isn't an option when the files are too big or the devices aren't connect to local network.
This sounds very similar to https://bugs.kde.org/show_bug.cgi?id=366795
Same report from an OnePlus 3/Fedora user: https://www.reddit.com/r/kde/comments/4z0pb1/cannot_copy_any_files_to_my_android_phone/
*** This bug has been marked as a duplicate of bug 366795 ***