Can't upload to webdav (Seafile 12 CE binary)

Dear Forum,

after upgrading from Seafile 11 to 12.0.11 (Ubuntu 24.04, binary version) I can’t upload via webdav. I can create directories. Uploaded files are visible but empty.

This is my conf/seafdav.conf

[WEBDAV]
enabled = true
port = 8888
fastcgi = false
share_name = /seafdav
workers    = 1

[fileserver]
# use_go_fileserver = true

And here is logs/seafdav.log

[2025-04-14 22:32:05] [INFO] wsgidav.wsgidav_app:583 127.0.0.1 - [MY_LOGIN] - [2025-04-14 20:32:05] "HEAD /" elap=0.038sec -> 200 OK
[2025-04-14 22:32:05] [INFO] wsgidav.request_resolver:179 Got OPTIONS '/' request
[2025-04-14 22:32:05] [INFO] wsgidav.wsgidav_app:583 127.0.0.1 - [MY_LOGIN] - [2025-04-14 20:32:05] "PROPFIND /" length=297, depth=0, elap=0.034sec -> 207 Multi-Status
[2025-04-14 22:32:05] [INFO] wsgidav.request_resolver:179 Got OPTIONS '/' request
[2025-04-14 22:32:05] [INFO] wsgidav.wsgidav_app:583 127.0.0.1 - [MY_LOGIN] - [2025-04-14 20:32:05] "PROPFIND /" length=297, depth=1, elap=0.046sec -> 207 Multi-Status
[2025-04-14 22:32:09] [INFO] wsgidav.wsgidav_app:583 127.0.0.1 - [MY_LOGIN] - [2025-04-14 20:32:09] "PROPFIND /webdav/" length=297, depth=1, elap=0.099sec -> 207 Multi-Status
[2025-04-14 22:32:10] [INFO] wsgidav.wsgidav_app:583 127.0.0.1 - [MY_LOGIN] - [2025-04-14 20:32:10] "PROPFIND /webdav/hallo/" length=297, depth=1, elap=0.083sec -> 207 Multi-Status
[2025-04-14 22:32:13] [INFO] wsgidav.wsgidav_app:583 127.0.0.1 - [MY_LOGIN] - [2025-04-14 20:32:13] "DELETE /webdav/hallo/signal-2020-09-19-001105.jpeg" depth=0, elap=0.126sec -> 204 No Content
[2025-04-14 22:32:13] [INFO] wsgidav.wsgidav_app:583 127.0.0.1 - [MY_LOGIN] - [2025-04-14 20:32:13] "PROPFIND /webdav/hallo/" length=297, depth=1, elap=0.051sec -> 207 Multi-Status
[2025-04-14 22:32:19] [INFO] wsgidav.wsgidav_app:583 127.0.0.1 - [MY_LOGIN] - [2025-04-14 20:32:19] "HEAD /" elap=0.020sec -> 200 OK
[2025-04-14 22:32:19] [INFO] wsgidav.wsgidav_app:583 127.0.0.1 - [MY_LOGIN] - [2025-04-14 20:32:19] "PROPFIND /webdav/hallo/" length=297, depth=1, elap=0.069sec -> 207 Multi-Status
[2025-04-14 22:32:19] [INFO] wsgidav.wsgidav_app:583 127.0.0.1 - [MY_LOGIN] - [2025-04-14 20:32:19] "PROPFIND /webdav/hallo/" length=297, depth=1, elap=0.051sec -> 207 Multi-Status
[2025-04-14 22:32:19] [INFO] wsgidav.wsgidav_app:583 127.0.0.1 - [MY_LOGIN] - [2025-04-14 20:32:19] "PROPFIND /webdav/hallo/" length=297, depth=1, elap=0.059sec -> 207 Multi-Status
[2025-04-14 22:32:20] [INFO] wsgidav.wsgidav_app:583 127.0.0.1 - [MY_LOGIN] - [2025-04-14 20:32:20] "HEAD /webdav/hallo/vault.cryptomator" depth=0, elap=0.051sec -> 404 Not Found
[2025-04-14 22:32:20] [INFO] wsgidav.wsgidav_app:583 127.0.0.1 - [MY_LOGIN] - [2025-04-14 20:32:20] "HEAD /webdav/hallo/masterkey.cryptomator" depth=0, elap=0.049sec -> 404 Not Found
[2025-04-14 22:32:20] [INFO] wsgidav.wsgidav_app:583 127.0.0.1 - [MY_LOGIN] - [2025-04-14 20:32:20] "HEAD /webdav/hallo/signal-2020-09-19-001105.jpeg" depth=0, elap=0.037sec -> 404 Not Found
[2025-04-14 22:32:20] [INFO] wsgidav.wsgidav_app:583 127.0.0.1 - [MY_LOGIN] - [2025-04-14 20:32:20] "HEAD /webdav/hallo/vault.cryptomator" depth=0, elap=0.060sec -> 404 Not Found
[2025-04-14 22:32:20] [INFO] wsgidav.wsgidav_app:583 127.0.0.1 - [MY_LOGIN] - [2025-04-14 20:32:20] "HEAD /webdav/hallo/masterkey.cryptomator" depth=0, elap=0.048sec -> 404 Not Found
[2025-04-14 22:32:20] [INFO] wsgidav.wsgidav_app:583 127.0.0.1 - [MY_LOGIN] - [2025-04-14 20:32:20] "HEAD /webdav/hallo/signal-2020-09-19-001105.jpeg/" depth=0, elap=0.032sec -> 404 Not Found
[2025-04-14 22:32:41] [ERROR] wsgidav.error_printer:91 Caught HTTPRequestException(HTTP_INTERNAL_ERROR)
Traceback (most recent call last):
  File "/[MY_PATH]/seafile-server-12.0.11/seahub/thirdpart/wsgidav/seafile_dav_provider.py", line 249, in end_write
    seafile_api.put_file(self.repo.id, self.tmpfile_path, parent, filename,
  File "/[MY_PATH]/seafile-server-12.0.11/seafile/lib/python3/site-packages/seaserv/api.py", line 294, in put_file
    return seafserv_threaded_rpc.put_file(repo_id, tmp_file_path, parent_dir,
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/[MY_PATH]/seafile-server-12.0.11/seafile/lib/python3/site-packages/pysearpc/client.py", line 127, in newfunc
    return fret(ret_str)
           ^^^^^^^^^^^^^
  File "/[MY_PATH]/seafile-server-12.0.11/seafile/lib/python3/site-packages/pysearpc/client.py", line 11, in _fret_int
    raise SearpcError(dicts['err_msg'])
pysearpc.common.SearpcError: Concurrent update

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/[MY_PATH]/seafile-server-12.0.11/seahub/thirdpart/wsgidav/error_printer.py", line 50, in __call__
    for v in app_iter:
  File "/[MY_PATH]/seafile-server-12.0.11/seahub/thirdpart/wsgidav/request_resolver.py", line 224, in __call__
    for v in app_iter:
  File "/[MY_PATH]/seafile-server-12.0.11/seahub/thirdpart/wsgidav/request_server.py", line 126, in __call__
    app_iter = provider.custom_request_handler(environ, start_response, method)
               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/[MY_PATH]/seafile-server-12.0.11/seahub/thirdpart/wsgidav/dav_provider.py", line 1620, in custom_request_handler
    return default_handler(environ, start_response)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/[MY_PATH]/seafile-server-12.0.11/seahub/thirdpart/wsgidav/request_server.py", line 738, in do_PUT
    res.end_write(with_errors=hasErrors)
  File "/[MY_PATH]/seafile-server-12.0.11/seahub/thirdpart/wsgidav/seafile_dav_provider.py", line 252, in end_write
    raise DAVError(HTTP_INTERNAL_ERROR, e.msg)
wsgidav.dav_error.DAVError: (500, 'Concurrent update')

[2025-04-14 22:32:41] [ERROR] wsgidav.error_printer:95 e.src_exception:
None
[2025-04-14 22:32:41] [INFO] wsgidav.wsgidav_app:583 127.0.0.1 - [MY_LOGIN] - [2025-04-14 20:32:41] "PUT /webdav/hallo/signal-2020-09-19-001105.jpeg" length=188239, elap=20.744sec -> 500 Internal Server Error

Thanks in advance for any ideas
Adrian