The AMP plugin provides a way to convert WordPress pages to AMP pages, but it can’t cover all third-party plugins or themes available for WordPress.
The third-party plugins are need to adopt the AMP framework in their plugin, if they add any such validation issues AMP plugin blocks those issues and shows as validation error to help site maintainer and developers fix them.
You can find more details in the below video.
What can you do?
1) You can find which plugin or theme is causing the validation issues using site scan or validation tool, contact the plugin author or theme author and ask them to adopt AMP in their plugin/theme.