An Auth Token will be revoked by eBay CS if eBay finds the user account in question was Takenover (ATO), and the account owner willreceive an alert email for the same. After the user account is restored by CS, the affected user can generate a new token and use it for making API calls.
If your new token gets revoked within a few hours again, chances are that there are a few things that may still need to be resolved e.g., ebay Customer Support may have detected an active item that was listed fraudulently and therefore ended the item which can possibly trigger a token revocation. Please reach out to the eBay CS team and work with them on ensuring that there are no other items or pending actions/ATO cases on your account that can trigger the token revocation.