Hi @link79,
1) Make sure you are running the latest Feed Them Social free version, currently 2.9.7.1
2) In your WordPress dashboard, go to Feed Them > Twitter Options and make sure that under Video Player Options, Show Videos is set to “yes”.
3) If you are running any caching plugins, manually clear those.
4) If you are running a JQuery plugin, you will want to deactivate it.
5) If you are running any Lazy Loading plugins, turn off lazy loading for the WP Page running the Twitter shortcode.
4) After the steps above, on the page where you have the Twitter shortcode, clear the FTS cache.
5) Now, if the above steps have not resolved the issue, then it is possible that another plugin or theme may be interfering. Try deactivating all other plugins besides the Feed Them Social plugins temporarily. Then test to see if it works. If this works, try reactivating them, one by one, to see which one is causing the issue.
If deactivating all plugins doesn’t help the issue try switching themes to one of the default WordPress themes then look at the page (this can be done under the Appearance tab of your install). It’s possible the theme is causing errors.
Let us know how it goes