This strange problem is happening at my company where some clients report issue with loading time. The temporary solution I provided was to use a proxy server (K-Proxy), the free service connects them via Canadian servers. U.S. servers are not free.
According to online research, this looks like some kind of security configuration at the hosting site. But We may not be using Cloudflare, the kind of security app some hosting site uses against DDoS attacks. This is done by changing DNS servers to Cloudflare's dns. Similar principle may have been applied to us.
The only solution is probably via hosting (of payroll.spgextranet.com) - networksolutions.com in this case.