The IP address you are using has been flagged as an open proxy. If you believe this to be incorrect, please visit https://help.instagram.com/
This can often happen due to popup blockers. Many popup blockers use an internal proxy mechanism and that is how they inspect/block traffic that generates the unwanted content.
If you have checked the LAN settings and don't have any proxy set, then try disabling your popup blocker for instagram. Or use another browser. Some browsers also use internal proxies, if you enable "little mode" since they use remote proxies to trim the fat from web feeds to provide a "lighter, less data required" page.
In Windows 10, to check for proxy, you can open your windows Settings -> Network and Internet -> Proxy and make sure no Manual proxy is configured.