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Please try the following additional troubleshooting steps:

Disable Full Screen Optimizations. To disable this, please find the "ffxiv_dx11.exe" and right click it and select properties. Then under the compatibility tab there will be a check box labeled "Disable Full Screen Optimizations". Check it and click apply.

Open the Nvidia Control Panel and going to 'Manage 3D Settings'. From here, select 'Program Settings' and select Final Fantasy XIV. You should see an option to select the GPU. Make sure it's set to your dedicated graphics card (it may be set to 'Auto' by default)

Delete locally saved content ('Documents' > 'My Games' folder), please note however this will remove all in-game configurations.
When the game is running, open the task manager, click the ‘Details Tab” Find the game and right click it. Select ‘Set Priority’ options to “High”

Double check to make sure PC is not over heating and remove any overclocks on GPU/CPU.

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