SUMMARY
The first copy of files to a local directory that I attempt from my Android phone, plugged into USB and using mtp, reliable works (yay!). But thereafter every file copy that I attempt fails.

STEPS TO REPRODUCE
1. Plug Google Pixel 2 into USB
2. On phone, Settings > USB Preferences > Use USB for, choose File Transfer.
3. In KDE Device Notifier, under choose the Open in File Manager that opens the mtp: protocol (usually the first action)
4. In the Dolphin that opens, navigate to Internal storage > DCIM > Camera
5. Split Dolphin's window, in second pane navigate to a local directory like /tmp.
6. Select some images in the phone pane, drag to second pane, choose Copy Here from pop-up menu.
7. Repeat step 6 with other files.

OBSERVED RESULT
The first copy succeeds, but thereafter copy always fails. For each file I get an alert
  Information
  Could not read file /Pixel 2/Internal shared storage/DCIM/Camera/THE_FILE_NAME.jpg

If I close Dolphin and disconnect the phone and verify that the mtp KIO is gone from `ps`listing, then repeat, I still get failures. I've tried using the other Open in Dolphin protocol (camera) and switching the phone's "Use USB for" to PTP, and still no luck. I'm able to copy again only after rebooting.

EXPECTED RESULT
Copy operations continue to work.

SOFTWARE/OS VERSIONS

Linux/KDE Plasma: Fedora 29 KDE spin
KDE Plasma Version: 5.14.4
KDE Frameworks Version: 5.53.0
Qt Version: 5.11.3

ADDITIONAL INFORMATION
When it was failing a few weeks ago December 2018, I got a different alert after a long delay,
  Error 150
or
  Unknown error code 150
  bad parameters

`journalctl` doesn't seem to have any relevant errors. I would be happy to reproduce this with debug settings or under gdb if it will help.