PHP errors with external storage provider STACK

[Obscurax]

Steps to reproduce

1. Add STACK as an external storage provider.
2. Upload files to STACK directly.

Expected behaviour

1. No PHP errors in the logs.
2. Files show up in Nextcloud.

Actual behaviour

I'm seeing PHP errors repeatedly, making it hard to analyze the logs when something else is wrong.
Once I remove STACK as an external storage provider the errors stop.

Syncing via clients and downloading/uploading via the Nextcloud web interface to the external provider is working. When files are uploaded to STACK directly they show up as 0kb in Nextcloud (web and clients).

Server configuration

Operating system:
Ubuntu 18.04.1 LTS
Web server:
nginx 1.15.8
Database:
MariaDB 10.3.12
PHP version:
PH 7.3.2-1
Nextcloud version: (see Nextcloud admin page)
Nextcloud 15.0.4
Updated from an older Nextcloud/ownCloud or fresh install:
Updated from 15.0.2
Where did you install Nextcloud from:
Shell script.
Signing status:

Signing status

No errors have been found.

Are you using external storage, if yes which one: local/smb/sftp/...
yes, WebDAV
Are you using encryption: yes/no
yes
Are you using an external user-backend, if yes which one: LDAP/ActiveDirectory/Webdav/...
No

Nextcloud log (data/nextcloud.log)

Nextcloud log

Error PHP	Undefined variable: response at /var/www/nextcloud/lib/private/Files/Storage/DAV.php#283
Error PHP	Undefined offset: 1 at /var/www/nextcloud/3rdparty/sabre/dav/lib/DAV/Xml/Element/Response.php#237
Error PHP	Undefined index: {DAV:}status at /var/www/nextcloud/3rdparty/sabre/dav/lib/DAV/Xml/Element/Response.php#236

I've found these issues on Github with similar errors: #11818 #1228

[noci2012]

And the WebDav issue with Alfresco was never cleared, now still on15.0.4......
(Sharepoint access also fails)....
Note: the Config screens show a green dot on the left of entries
The File handler complete fails.

[noci2012]

AFAICT these error are related:
Error cron TypeError: Argument 1 passed to OCA\GroupFolders\Versions\VersionsBackend::getVersionsFolder() must be of the type integer, string given, called in /.../htdocs/apps/groupfolders/lib/Versions/VersionsBackend.php on line 154 21 minutes ago
Error PHP Array to string conversion at /.../htdocs/lib/private/App/DependencyAnalyzer.php#356 24 minutes ago
Error PHP Undefined offset: 1 at /data/WWW/.../htdocs/3rdparty/sabre/dav/lib/DAV/Xml/Element/Response.php#237 24 minutes ago
Error PHP Undefined index: {DAV:}status at /.../htdocs/3rdparty/sabre/dav/lib/DAV/Xml/Element/Response.php#236 24 minutes ago
Error PHP Undefined offset: 1 at /.../htdocs/3rdparty/sabre/dav/lib/DAV/Xml/Element/Response.php#237 24 minutes ago
Error PHP Undefined index: {DAV:}status at /.../htdocs/3rdparty/sabre/dav/lib/DAV/Xml/Element/Response.php#236 24 minutes ago

[skjnldsv]

Still occurring?

[ghost]

This issue has been automatically marked as stale because it has not had recent activity and seems to be missing some essential information. It will be closed if no further activity occurs. Thank you for your contributions.