NextCloud 12: Some programs ask for user auth data twice

Nextcloud version: 12.0.0
Operating system and version: Debian Linux 8.8
Apache or nginx version: Apache 2.4.10
PHP version: 5.6.30
Is this the first time you’ve seen this error?: Yes, after updating from NextCloud 11.0.2

I use the following script to map a WebDAV folder to drive N: on Windows 7 and Windows 10:

  set username=XXX
  set password=YYY
  set drive=N:

  NET USE %drive% https://<SERVER>/remote.php/webdav/ %password% /USER:%username%

  set /p=Press ENTER to continue...

  exit 0

I can perform all file management tasks (file copy, move, delete) correctly, both with the Windows Explorer and a file manager called DoubleCommander. But when I try to open a Word file with MS Word 2016 or a PDF file with Adobe Acrobat DC (Version 17), I get again the authentication dialog - with the relevant data already present (username and password). If I confirm, the Word or the PDF file are opened correctly. The same happens if I do not confirm the authentication data, but in this case it takes longer to open the file.
Disturbingly enough, when I try to open the Word file with LibreOffice Writer or SoftMaker Office Professional 2016, and the PDF document with SumatraPDF, everything works correctly.
I’ve tried the patches described at

and at


but the authentication dialog box still gets displayed.
In the NextCloud log under Admin > Logging I only see the following error:

Array to string conversion at /srv/vhosts/enubes/www/lib/private/legacy/l10n/string.php#72

Under NextCloud 11.0.2 the WebDAV access was working correctly.

Is there a way to fix this problem?

Thanks for any hint!

cpix

I’ve updated the NextCloud installation to version 12.0.1.15 and the problem is still there.
Does anyone have a hint about how to solve this disturbing problem?