It's probably that there's a network issue somewhere between you and the SE servers. To confirm this you'd need to do a traceroute at the time you're having an issue. For Cactuar you can use the IP 204.2.229.9 which will show your route to the Aether datacentre.

Unfortunately if it is a consistent routing problem you'd have to lean on your ISP to change your routing (they probably won't) or use a 3rd party VPN service to do it for you, but one thing at a time, best to confirm this is actually the issue first.