Hello,
1,2. It’s a lazy loading functionality for images and seems that it comes from a third-party plugin, therefore you can disable this functionality via the plugin’s settings.
So I suggest you deactivate all plugins that are not related to our theme and then activate the plugins one by one, checking the issue to detect which one causes the problem.
3. Yep, it affects the website speed.
Please let me know if you have any further questions in the meantime.
Kind Regards