[solved] Some files cannot be found after server upgrade

After my server upgrade 5.1.11pro --> 6.0.2 pro everything looked fine but now I have a weird problem. If I use the web browser it shows all my files but when I try to open/view some pictures I get an error The image could not be loaded (the preview is broken too) or File does not exist.
But the weird thing is, that some of files are accessable without any issues. I can not see a pattern for this behaviour.
./seaf-fsck.sh showed no errors, nevertheless I have run it with the repair option on any repo.

seahub_django_request.log shows a lot of warnings and an error:

2016-10-31 16:06:29,199 [WARNING] django.request:170 get_response Not Found: /error_docs/maintenance.html
2016-10-31 16:06:32,078 [WARNING] django.request:170 get_response Not Found: /error_docs/maintenance.html
2016-10-31 16:06:45,123 [WARNING] django.request:170 get_response Not Found: /seafhttp/repo/db1633f2-5156-4c6e-8/error_docs/maintenance.html
2016-10-31 16:11:03,237 [WARNING] django.request:170 get_response Not Found: /repo/90593a8b-8149-4759-83b6-10245c007642/raw/Bilder/LR%20Export/IMG_0945_003.jpg
2016-10-31 16:11:03,260 [WARNING] django.request:170 get_response Not Found: /repo/90593a8b-8149-4759-83b6-10245c007642/raw/Bilder/LR%20Export/IMG_0946_004.jpg
2016-10-31 16:11:03,263 [WARNING] django.request:170 get_response Not Found: /repo/90593a8b-8149-4759-83b6-10245c007642/raw/Bilder/LR%20Export/IMG_0947_005.jpg
2016-10-31 16:15:32,434 [ERROR] django.request:256 handle_uncaught_exception Internal Server Error: /office-convert/static/90593a8b-8149-4759-83b6-10245c007642/6c8c5aa9b4e063$
Traceback (most recent call last):
  File "/var/www/vhosts/seafile/subdomains/seafile/seafile-pro-server-6.0.2/seahub/thirdpart/Django-1.8.10-py2.7.egg/django/core/handlers/base.py", line 132, in get_response
    response = wrapped_callback(request, *callback_args, **callback_kwargs)
  File "/var/www/vhosts/seafile/subdomains/seafile/seafile-pro-server-6.0.2/seahub/seahub/views/file.py", line 1507, in office_convert_get_page
    file_id = _office_convert_get_file_id(request, repo_id, commit_id, path)
  File "/var/www/vhosts/seafile/subdomains/seafile/seafile-pro-server-6.0.2/seahub/seahub/views/file.py", line 1464, in _office_convert_get_file_id

Edit: I have solved the problem by myself. It is no seafile problem, but an apache problem. My folder and file names got spaces and german umlaute (ü,ö,ä,ß). When I remove or replace the spaces/umlaute everything works fine again - that’s a mean apache bug.

Edit2: For further information read this