Other
Repairing the Client
How to check for missing files or files damaged by data corruption
The different clients each have their own procedures to launch a scan for data corruption.
Steam
Right-click on Path of Exile in your Steam Library
Click on Properties...
Click on Installed Files
Click on Verify integrity of installed files
Standalone (Windows)
Go to the game's main install directory
The default is %ProgramFiles(x86)%\Grinding Gear Games\Path of Exile
Copy and paste the above right into File Explorer's address bar!
Double-click on PackCheck.exe
Standalone (macOS)
There is no known method for this client on this OS.