features Articles = Error 404 in Joomla

Unfortunately another mistake. I reinstalled a Joomla 3.10. Template first Protostar.
Created a new post as "Test".
Menu set up (Main Menu).
Only one menu entry = Home.
This menu item defined in menu item type = single articles.
Additional default page = yes.
Everything works!
Now the menu item defined in menu item type = features articles
The individual article on features = yes.
Is working!
Ok - now installed the newly created Nicepage theme and the Nicepage plugin for Joomla 3. Set the new theme as default and set the new module position (hmenu) for the menu.
Everything works.
But ... now created a new page with the Nicepageplugin. A simple text. Saved - and ..... the menu item type = feature Articles no longer works! A 404 error comes up.
If I change the menu entry to = single Articles, the entered page is displayed correctly again.
However, when I set up the template again on Protostar (with the changed module position of the menu), everything works. So it must be the Nicepage template and/or the Nicepage plugin.