I dont know if this a webdav problem or a nextcloud problem but im having problems with open old documents (.docx. .pdf etc) Creating new and edit them is no problem. However the old ones cant be opend?
Im running nextcloud connected to our AD server and the files im trying to open are stored on one of our fileservers mapped as an cifs share inside nextcloud.
Can you check your logfiles? A reason could be that your file-index is not up to date (should be in general) and the file doesn’t exist any more. Or if it was shared, there have been some problems and you should first upgrade to the latest version https://nextcloud.com/changelog
This problem has been resolved, as you said it was some problem with the files had been moved around or renamed. Anyway it’s been resolved.