On Steam...  Right Click Ark and select Properties
Then click "LOCAL FILES" and "Verify Integrity of game files..." Integrity of game files..."

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On EPIC  

Click the three dots underneath Ark and choose "Manage"
Then click "VERIFY"

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On Windows, it's worth doing a system check regardless of the outcome of the above.
In an Administrator command prompt, run   sfc /scannow

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If the above command says it found errors that it couldn't fix, then run the following commands...

DISM /Online /Cleanup-Image /CheckHealth
DISM /Online /Cleanup-Image /ScanHealth
DISM /Online /Cleanup-Image /RestoreHealth