Social Media Link Preview Validators
If a link preview is showing up incorrectly, please run it through the appropriate link validator for the social network. Usually, once you clean it up for one, it's correct on the rest, but as every network has slightly different image sizes, make sure you validate for each of them to ensure that the link preview is displaying as you want it to.
Facebook Sharing Debugger — make sure you're on the Sharing Debugger tab (not Webmaster or Batch Invalidator)
Note: It can take a few minutes for updated link preview/meta information to flow through to the validators.