I wish I did.
All I know is that a remarkably high number of people are having trouble with the ftpupload.net hostname. As far as I can tell, the hostname itself is working fine, but the domain is blocked by various virus scanners and security filters. If you use a VPN, you can usually bypass those and see that the hostname itself worked.
Who has actually blocked this domain name and why is not clear to me. I also don’t know if they blocked the domain because they somehow got the idea that our hosting is dangerous, or just because the domain had a bad history before we got it.
I don’t know who to ask or how to ask them, whether this is something we can do something about or whether this is just a big misunderstanding.