Hi Daniel,
Please make sure the User Profile > Disable Attribute Mapping option is not set while using Custom Attribute Mapping.
To check custom mapped attributes you can go to User Management and select logged-in user.
Here you will get to see a Properties section with a list of key and value pairs. These key and value pairs are nothing but your custom attributes which you must have mapped in the plugin.
Please note the custom attribute mapping only affects after Single Sign On.
Let me know if this helps.
Thanks,
Shradha