There are many threads all over the forums about this issue and there is not a single reply from SE about it.

I am having issues with or without using WTFAST. I am getting 4-5 second lag spikes in EX primals, making them unplayable. It's not my PC, it's not my ISP, it's not a setting that needs to be changed. It's your servers/network. This is absolutely ridiculous for a game with a monthly subscription. Everything else works fine. Verizon is not throttling this game neither is any of their partners. It's your ISP and/or Servers. Please fix this ASAP or you are going to lose many customers. I really want to enjoy this game but every single day I am dying due to a lag spike or latency. I can go play any other MMO that exist right now and not have this issue.

Win8
I72600k
680 gtx
Vertex 3 SSD
Verizon FIOS
Buffalo, NY