The completion files installed with Kile are located in /usr/share/apps/kile/complete/{tex,dictionary,abbreviation} but Kile thinks no files are present. 

For files previously enabled, it says "File not found". However, it allows me to check the boxes for these and, once I check them, completion works for the relevant commands until Kile forgets them again. 

If I try to 'Add...' completion files, the list of possibilities is empty. I do seem to be able to 'Remove' files, however, though I am reluctant to do this much as they are then gone forever.

I have never had any custom completion files and I have never enabled dictionary or abbreviation files. If I try to 'Add...' any, these lists are also empty.

~/.local/share/kile/complete is empty. If I remove the empty directory, it is recreated automatically. 

I cannot find anything obviously helpful in .xsession-errors (but may not be looking for the right thing). All I can find in the journal is information about Kile's window management from kwin.

Reproducible: Always

Steps to Reproduce:
1. Open configuration dialogue and choose the 'completion tab'
2. Observe 'File not found' - try 'Add...'
3. Check some of the not found files and choose 'OK'
4. Now open the configuration dialogue for Kile again. Open any tab (need not be completion). You don't need to change anything. Just hit 'OK'.
5. Repeat steps 1-3 and then restart Kile.

Actual Results:  
At 2. Files are not found although they exist. Add... gives an empty list.
At 3. Completion is re-enabled for those particular groups of commands for a while. 
At 4. Completion is entirely disabled again.
At 5. Completion is entirely disabled again.

In some other cases, completion is entirely disabled but I'm not sure of the triggers. 

The list of 'LaTeX Commands' in the side-window is affected in just the same way as completion. The commands appear when the (not found) files are re-enabled but disappear if the configuration dialogue is opened and 'OK' is chosen, the application is restarted or some other trigger causes completion to be disabled.

Expected Results:  
The files in /usr/share/apps/kile/completion/{tex,dictionary,abbreviation} should be found.
Enabled completion files should stay enabled (unless I choose to disable them, of course).
It should be possible to add additional files using the 'Add...' dialogue which should list the possible options from the files in the above directories.
The list of LaTeX Commands in the side-window should behave similarly.

~/.kde4/share/apps/kile is a symbolic link to ~/.local/share/kile, in line with my distro's recommendations for transition between KDE 4 and Plasma 5.  Similarly, ~/.kde4/share/config/kilerc is a symbolic link to ~/.config/kilerc.