@PeterJones I was able to replicate the issue you had and tried to see if there is a resolve as to why an edited xml file cannot be seen for an existing file loaded in the NP++ editor.
Inserting a brand new xml (dcl.xml) into the autoCompletion folder everything worked as expected.
Closing NP++ then replacing the xml file with an edited version, then reopening NP++, the file did not recognize the edited xml at all!
Close the file, clear the recent files list, then closing NP++ and finally double-click to open the file, the edited xml was not recognized.
However, if the file exists but has no characters inside, the edited xml can be seen.
By beginning a new file, the edited xml file can be seen.
One item I did not try is to relocate the file in a different folder, then double-click in the file manager to open.
Another I did not try is to close NP++, delete the edited xml file, open NP++ (with file present), close NP++, reinsert the edited xml into the autoCompletion folder then reopen NP++.
For now the only resolve when an edited xml file replaces another in the autoCompletion folder is to start a new file in the editor to check the work…
Hope this helps.