Sending/receiving pictures/data for exact two users not working, works for other users fine

Description:

Two users out of 20 can not see images / data send from them to others or received from others.
For all other users, it works fine.

Steps to reproduce:

Send image or datafile from clipboard to chat. But it seems, that this is not reproducable in a standard installation. May there is something broken in our database.

Expected behavior:

Show the real screenshot, not a "retry" picture.
Or show the real datafile, which can be downloaded.

Actual behavior:

Send a screenshot from clipboard always shows this in the chat.

When trying to download this screenshot-file by the download button, the following message appears:
Der Zugriff auf chat.xxxxxxxxxxxxxxxxxxxx.de wurde verweigert Sie sind nicht zum Aufrufen dieser Seite autorisiert.
HTTP ERROR 403

This happens only for the two users, but in all chats (can not open send and received pictures / files)
All other users see the pictures / files.

Server Setup Information:

• Version of Rocket.Chat Server: 3.16.2
• Apps Engine Version: 1.27.1
• Operating System: Debian GNU/Linux 10 (buster) Linux 4.19.0-17-amd64 #1 SMP Debian 4.19.194-2 (2021-06-21) x86_64 GNU/Linux
• Deployment Method: tar
• Number of Running Instances: 1
• DB Replicaset Oplog:
• NodeJS Version: v12.18.4
• MongoDB Version: 4.2.14 / wiredTiger (oplog Enabled)

Client Setup Information

• Desktop App or Browser Version: Browser Version: Chromium Version 91.0.4472.114 (Offizieller Build) Arch Linux (64-Bit)
• Operating System: Manjaro Linux

Additional context

We are using LDAP, but this seems to work, because the 2 users can log into their account and work with the chat.
File upload from all users (also this 2) is working, because others can download their send files.
But this 2 users can not open their own send files/pictures and received files/pictures from others.
Seems to be a problem with access to the database.

the two users are "verified" users.

This option is set per default to True
Protect Uploaded Files = True (Only authenticated users will have access)

When setting this option to False, data handling works for all users

Any hints there what to check next?

Relevant logs:

No relevant logs found on server.

Start with the Protect Uploaded Files setting and reproduce the 403 for the two affected verified users, comparing their access with users who can open the same files. Trace the upload download path and authentication behavior; done means affected users can view and download sent and received images and data files while protection remains enabled.