Steps to reproduce:
1. Create a page template
2. Change to the configuration mode of the page
3. Add a portlet where you can change the scope (tested with the 'Tag Cloud' portlet and the 'Web Content Display' portlet
4. Change the scope of the portlet to the page (Configuration > Scope > Page Name)
5. Create a page inheriting from the template
6. Change to the created page
The name of the portlet now contains javax.portlet.title.XYZ instead of the actual name. I don't know whether the problem exists with more portlets. The blog portlet e.g. works this way.
I tested it with a clean installation of Liferay 6.2.3 CE GA4.