Generators and Titles created on Motion are not working in FCP

This suggests to me that your version of Motion is too new compared to the version of FCP.

Please tell us exactly which version of each application you have.

If in doubt, go to Final Cut Pro->About Final Cut Pro, and similarly for Motion.

As Tom suggests, double-check your installation in the Motion Templates folder. This excellent guide from fellow list member Fox_M can help.

How to manually install 3rd party Motion template.  https://fcpxtemplates.com/installing-plugins-for-fcpx/

They're all Pixel Film created generators? You should contact the developer. Make sure they're installed correctly in the Motion Templates folder.

Can you show your category and your Generator selected in the Generators browser?

Also, show in column view in the Finder where the generator is stored.