Upload via Android App suddenly gives an error on one phone (<DE> "Ordnerfehler" and "Server not found")

Nextcloud version (eg, 18.0.2): 19.0.3
Operating system and version (eg, Ubuntu 20.04): Ubuntu 20.04
Apache or nginx version (eg, Apache 2.4.25): 2.4.41
PHP version (eg, 7.1): 7.4.3

The issue you are facing:
Uploads with the Android App suddenly began to fail all the time. First you see the progress-bar empty for a few seconds, then you see a pop-up “Server nicht gefunden // Server not found” and in the Upload section “fehlgeschlagene Uploads // Failed Uploads” you see the uploads with the tag “Ordnerfehler // ??”. Download works fine.
On other phones and in browser/desktop the upload works.

I allready tried to reinstall, but the problem is still there.

Is this the first time you’ve seen this error? (Y/N): Yes

Steps to replicate it:
No idea.

The output of your Nextcloud log in Admin > Logging:

No related errors

The output of your config.php file in /path/to/nextcloud (make sure you remove any identifiable information!):


The output of your Apache/nginx/system log in /var/log/____:


Same issue, cannot upload in android aplication. “Server not found”.

Ubuntu 18.04
Nexcloud 20.0.13
Apache/2.4.29 (Ubuntu)
PHP 7.2.24