Hi — it looks like this is being caused by the head template ({{head|mul|symbol|head=''M''_🜨}}). Removing that template and previewing the page shows the expected page title formatting

Thank you!

The explanation is that the display title {{DISPLAYTITLE:''M''_🜨}} was placed before the {{head|mul|symbol|head=''M''_🜨}} template, and the module (Module:headword ) invoked by the template provided a conflicting display title <span class="Latn">M🜨</span> in Lua (frame:callParserFunction("DISPLAYTITLE", display_title)). The module gets a return value that is a warning that renders like Warning: Display title "<i>M</i>_🜨" overrides earlier display title "<span class="Latn">M🜨</span>"., but doesn't print it. It probably should.

I gather the warning is text emitted by the parser function so that you can tell what wikitext triggered the warning, but it would be nice if the warning were visible elsewhere or the page were put in a category so that display title problems can be more easily located and debugged. I can change the module to print the warning, but there's no way to tell how many pages will display warnings after I do that.

I think a category would be a good solution. The category would have to be added by the parser and not by the wikitext of the message, to track cases where the warning is generated but isn't shown by a template. However, even with a category, it would sometimes be hard to find which templates actually changed the display title, generated a warning, and didn't display the warning. I am not sure what the solution would be for that.

Incidentally there does not seem to be a MediaWiki message page that I can edit to change the message (uselang=qqx version of the a revision with the error).