If your staff are located in Mainland China and Seafile app doesn't sync properly, try updating Seafile Syncing Apps settings.
Instead of https://app.nihaocloud.com server address, change it to:
as the new server address and it should fix syncing issues.
Why HTTP instead of HTTPS?
You can add https as well, but keep in mind that GFW filters all encrypted (https) traffic and might slow down upload/download speed.