Good morning and thank you for posting on the Final Fantasy XIV Technical Support Forums.

The game doesn't seem to be able to utilize all of the cores you have. When did this start happening? Did anything change/update on your PC that coincides with this?

You mentioned this happens after a set amount of time, does the location in the game affect it at all? Does selecting DX9 mode have the same issue?

There is something I'd like you to check. Open the Task Manager (Ctrl + SHIFT + Esc) and go to the 'Details' tab. Find Final Fantasy XIV (It should be listed as 'ffxiv_dx11.exe' or 'ffxiv.exe') and right-click it. Select 'Set Affinity' and makes sure all the processors are selected (you should see '' and 'CPU 0' through 'CPU 7' for an 8-core CPU).

We hope we can be of assistance in helping you enjoy the exciting world of Final Fantasy XIV!