Unity refuses to show new Splash Screen settings

[xrm0]

I have a project created same years ago which I’ve been upgrading as Unity released new versions. Using 5.5.2f1, and having a Unity Personal edition the show splash screen button is disabled and it shows the legacy splash screen options:

But if I open a project created with 5.x (5.0 or 5.1) it looks like this:

What’s going on?

[xrm0]

Tried 5.6.0f1 and the problem persisted.

Removing ProjectSettings/ProjectSettings.asset solved the problem (lost all the project settings, but at least got the new splash screen settings).