took a quick look, aren't those backlinks to subdomains? No idea what the product/service does but it appears subdomains are the main spam links, not the root.. So perhaps they were duped by spammers creating subdomains
It is possible that on that fateful day, Google noticed zlio is user generated sub domains, and lost power.
subdomains are treated as separate domains, right
If all the subdomains had links back to zilo (say the header or footer), it starts to look like a huge link farm, or a bunch of satellite sites. It's actually pretty dangerous. But disavow is here, right? hah