On our website there are some key users that can register other users for events from the front end, using the 'manage registrants' menu option.
In the registration screen, there is a dropdown to select the user. This is no longer working since the recent joomla update (3.10.1) --> Error '404 View users not found'
In the back-end, this functionality is still working.
I first thought it might be related to the 'Helix Ultimate' template that I am using, which is causing some other problems.
But when I switch to Protostar or Beez3 tempates, I still get the error in the front end.
It might be because a folder was lost for some reasons (the view for displaying users for selecting). You can submit a support ticket sending us super admin account of your site and link to that registrants management page. We will check to see why it happens and get it sorted