Hi linae,
Okay so that suggests something you have installed is removing this option and enforcing it as we do not force users to use Parallax.
I’m not too sure what is doing this so I would recommend running a plugin conflict test. This is not to suggest this is a plugin conflict (it’s not), only that this is a good way of figuring out what plugin/theme is doing what.
For reference, here are our typical plugin conflict test steps:
You can start by disabling all non-SiteOrigin plugins and see if this fixes the issue. You’ll need to clear all your caches after disabling your plugins. So just to confirm, double check if the issue is coming up while all other plugins are disabled.
If it does fix the issue, then try re-enabling your plugins one by one until the issue comes back. This procedure will help diagnose which plugin is causing the issue. Once we know that, we’ll be able to look at what might be causing the conflict and either solve the problem or help you find an alternative plugin.
You could also try temporarily switching to a default WordPress theme like Twenty Sixteen. Default WordPress themes are generally very light weight which lowers the chance that they’ll conflict with plugins, so they’re a good way to test if your original theme is the source of the issue.