some files are missing in the scripts folder
cp -R seafile/seafile-pro-server-6.3.2/seahub/media/assets/scripts/app seafile/seafile-server-latest/seahub/media/assets/scripts
did solve the problem
[EDIT]
sysadmin-app fiolderr is also missing
cp -R seafile/seafile-pro-server-6.3.2/seahub/media/assets/scripts/sysadmin-app /seafile/seafile-pro-server-6.3.4/seahub/media/assets/scripts/
With memcached activated, i still have the same error (BrokenPipe) at first startup but the webUi is displayed
The mecmached error does not occur anymore