Yes, that is a transient error that I have seen since converting SemanticTitle to use display title under the hood. It has to do with the way the parser sets page properties. SemanticTitle really should not be trying to set display title page property itself, since the parser owns page properties. I initially thought this was a one time problem that could occur when upgrading to the new version of the extension. I was not aware that it is an on-going problem for new pages.

Fortunately, there is a quick fix: you can change from setting the display title with a property to using {{DISPLAYTITLE:...}} to set it. You would also need to change your configuration to remove $wgSemanticTitleProperties. You could obviously continue to set the property if you use it for other purposes.

I'm actually considering removing the feature of setting the display title from a Semantic MediaWiki property or Cargo field from an upcoming release of SemanticTitle. It duplicates the functionality of the {{DISPLAYTITLE:...}} magic word that is built into MediaWiki - and it duplicates it in an inferior manner. SemanticTitle would still retain the functionality to change the link text on a page to the display title (unless/until I can get that functionality accepted into MediaWiki core, disabled by default with a configuration variable) and the #semantic-title parser function. I welcome your feedback on this potential change. I would make this change when I release a new version of SemanticTitle to work with MediaWiki 1.27. I had a new PageProps class merged into MediaWiki core recently, which will improve SemanticTitle's read access to the display title page property.

Hi,

I've tryed to follow your proposal and use {{DISPLAYTITLE:}} to set the new title, but I also need to set $wgRestrictDisplayTitle = false;.

The official documentation:

The value must be equivalent to the default title: only capitalization changes to certain parts of the title (not all) and replacing spaces with underscores are allowed (this can be changed with $wgRestrictDisplayTitle).

Oh, yes, I'm so sorry - I should have mentioned that. You need to set:

$wgAllowDisplayTitle = true;
$wgRestrictDisplayTitle = false;

to use the {{DISPLAYTITLE:...}} approach.