Media in shared folders (share link) does not load

[AnKosteck]

Describe the bug
The issue is that media inside a folder shared via a share link cannot be loaded. For now I know that movies (e.g. mp4, mov) and images (.png and .jpg) are affected.
Existing bug entries for the files_videoplayer app (e.g. nextcloud/files_videoplayer#130 or nextcloud/files_videoplayer#159) seem do hint in that direction but they do not describe our problem accurately.
The very same images or videos can be played or displayed when accessed normally through your files library so this does not seem to be a general file format issue.
Curiously enough said media can be loaded when shared directly via share links instead from inside a folder.

We operate a productive and a test environment of Nextcloud, both are at version 18.0.6 and this is reproducible on both instances.
Nextcloud does not seem log anything. The only hint I can give is the return value the browsers give: 401

To Reproduce

1. Create a folder
2. Put in some data (text files, documents, images, videos etc.)
3. Create a share link for said folder
4. Try opening the files via the share link
   4.1 Everything except images and videos can be loaded and displayed
   4.2 The loading screen is shown instead of showing the image or video

Expected behavior
Images and Videos should be loaded and shown just fine.

Screenshots
Well, the loading screen...

Desktop (please complete the following information):

• Browsers: Chrome 84.0.4147.89; Firefox 68.10.0esr, Edge (old and new), ...
• Operating system: Windows 10 64bit 19041.388 (2004)

Browser log

Error: "Request failed with status code 401"
    exports createError.js:16
    exports settle.js:17
    onreadystatechange xhr.js:61
Viewer.vue:391

[skjnldsv]

Have you enabled federated sharing on your server?

[AnKosteck]

No, federated sharing is disabled. Is that now a requirement for stuff like this?

[AnKosteck]

Or maybe a list of all enabled apps:

Enabled:
  - accessibility: 1.4.0
  - activity: 2.11.0
  - admin_audit: 1.8.0
  - cloud_federation_api: 1.1.0
  - comments: 1.8.0
  - dav: 1.14.0
  - federatedfilesharing: 1.8.0
  - files: 1.13.1
  - files_pdfviewer: 1.7.0
  - files_rightclick: 0.15.2
  - files_sharing: 1.10.1
  - files_texteditor: 2.11.0
  - files_trashbin: 1.8.0
  - files_versions: 1.11.0
  - files_videoplayer: 1.7.0
  - logreader: 2.3.0
  - lookup_server_connector: 1.6.0
  - nextcloud_announcements: 1.7.0
  - notifications: 2.6.0
  - oauth2: 1.6.0
  - onlyoffice: 4.3.0
  - password_policy: 1.8.0
  - piwik: 0.5.4
  - provisioning_api: 1.8.0
  - recommendations: 0.6.0
  - serverinfo: 1.8.0
  - settings: 1.0.0
  - sharebymail: 1.8.0
  - systemtags: 1.8.0
  - text: 2.0.0
  - theming: 1.9.0
  - theming_customcss: 1.6.0
  - twofactor_backupcodes: 1.7.0
  - updatenotification: 1.8.0
  - user_ldap: 1.8.0
  - user_saml: 3.1.2
  - viewer: 1.2.0
  - workflowengine: 2.0.0
Disabled:
  - encryption
  - federation
  - files_external
  - firstrunwizard
  - photos
  - privacy
  - support
  - survey_client

On the sharing settings page everything but search global or public address book for users is unchecked.

[skjnldsv]

No, federated sharing is disabled. Is that now a requirement for stuff like this?

yep! Please enable it again :)
They use the same endpoint for public shares and you cannot directly access the files if not enabled