Howto debug up/downloading via webinterface fails


I have setup 2 identical servers based on Linux debian with apache for 2 different groups of users.
1 group has issues with up/downloading via webinterface, while the other group has no issues
Server 1 Uploading fails, and when a file is uploaded through the feafile client or seadrive the files don’t show through the web interface.

When i compare config and logfile between the to servers i don’t find anything usefull.
So i would like to learn how i find the cause of the limited use through the webinterface (i guess apache with seafdav??) while everthing with the seafile client is OK.
I checked apache log but don’t find anything usefull.

Any advice appreciated
Kind Regards

I found out that if the system settings below are not correct this problem allso occur.
However, this not my solution.

I checked if system admin/settings/url settings for FILE_SERVER_ROOT & SERVICE_URL are correct.

Kind Regards