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If this is only affecting one character, then it may be something to do with your locally-saved settings. Go to 'My Documents' > 'My Games' > 'Final Fantasy XIV' and delete that folder. If there are any corrupted files that are associated only with that character, this will get rid of them.
If this does not solve the issue, try updating your graphics card drivers and doing a clean boot.
To do a clean boot simply open the task manager and select the 'Start up' Tab.
Disable everything here and restart the PC. This will make sure that no background processes are interfering with the game.

I would also like to suggest the following methods below to help resolve the issue.
- Uninstall the game and delete the installation folder. Then reinstall the game directly through the Steam Library.
- Delete or rename the "etc" folder that exists within the game's installation folder. Please also check the game folder in "My Games" as well.

Below are the default locations for the installation folder:
- Standard Windows version -
C:\Program Files (x86)\SquareEnix\FINAL FANTASY XIV - A Realm Reborn
- Steam version -
- C:\Program Files (x86)\Steam\steamapps\common\FINAL FANTASY XIV Online

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