Created attachment 154201 [details]
screenshot of "about system"

SUMMARY

after opening a folder containing >2000 images, mark all (ctlr a) and delete (shift del) dolphin starts deleting files - but after a few seconds it stops with following error message (in German):

Interner Fehler
Bitte senden Sie einen ausführlichen Problembericht an https://bugs.kde.org
Unbekannte Fehlersituation: [16] Das Gerät oder die Ressource ist belegt

---> 
the files (images) to be deleted are on a network drive. Dolphin is configured to show previews on network drives too!! Because previews are build up slow and still during deletion I guess the cause of the error is that dolphin will read an image (for creating the preview) that it is already deleted.
When changing the configuration to not build previews this error does not appear!!

STEPS TO REPRODUCE
1. open a folder with many files (images)
2. mark all and delete the images (during preview is build up)
3. Dolphin will stop with error message 

OBSERVED RESULT
Dolphin produced error while deleting files

EXPECTED RESULT
no error should appear - all files should be deleted

SOFTWARE/OS VERSIONS
Windows: 
macOS: 
Linux/KDE Plasma: Manjaro
(available in About System)
KDE Plasma Version: 
KDE Frameworks Version: 
Qt Version: 
---> see attached screenshot






ADDITIONAL INFORMATION