This week i found out that there was a limit on the size of the zip files that can be generated/downloaded . In the manual i’ve found the solution and changed the settings in Seafile.conf.
In seafile.conf:
[fileserver]
Set maximum upload file size to 200M.
max_upload_size=200
Set maximum download directory size to 200M.
max_download_dir_size=200
Luckily I had access to the server remotely (ssh) but it would be nice to have this, and maybe more, settings in the admin interface.