Symfony\Component\Routing\Exception\MissingMandatoryParametersException:

Reporting same issue here. On a brand new site with only devel and name contribs installed, when opening 'name list formats' at /admin/config/regional/name/list, page returns "The website encountered an unexpected error. Please try again later." and the following log:

Symfony\Component\Routing\Exception\MissingMandatoryParametersException: Some mandatory parameters are missing ("name_format") to generate a URL for route "entity.name_list_format.devel_load". in Drupal\Core\Routing\UrlGenerator->doGenerate() (line 187 of /app/web/core/lib/Drupal/Core/Routing/UrlGenerator.php).

/admin/config/regional/name/list is the admin path in question, not /admin/config/regional/flexdate/list in the ticket description above.

I ran into this issue as well. I found that the issue stems from a difference in the name_list_format links defined in the Name List Format configuration entity class and the name.routing.yml.

The attached patch resolves this.

I was able to reproduce this issue after installing devel module with field name module in drupal 10.1.
After applying the above patch, the issue was resolved. I have attached the screenshot for reference.

+1 for RTBC

Thanks. This patch works for me as well.

Thanks for your contributions.

Automatically closed - issue fixed for 2 weeks with no activity.