Featured Image Cache

Hello, I am having an issue with my Featured Images not refreshing when changed. I currently have removed all Featured images from my pages. I am using the plugin Comet Cache and have used the manual clear feature. I tried deactivating Comet Cache. I tried reinstalling Comet Cache. I have cleared my browser cache. I have rebooted my cable modem. I deleted the images from the media library. Yet, when I share to social media platforms, the old image (thumbnail) still appears. Note. This problem only applies to images. All other content updates fine. Any help you can offer would be appreciated. Regards, Paul Stuart, ve3eby.ca