Perhaps you could try the following:
1) Remove the relationship you in the datasources.
2) Create a group field in the 'User Points Earned' datasource for 'User group'. (I would prefer to do it in my database itself, if you can't do it in Tableau)
3)Create a dashboard with the two sheets and add a filter action.
4)In the action, under Target fields map 'User' from (Sheet 1) to the 'User Group' (the field you just created) in the other datasource.
It worked for me for all the first values in the group not for the others. Probably its a string field issue with the extra spaces.
Also try to map it to groups itself, this might also work.
This might not solve it completely but might help you a little.
Thanks, Aiswarya. I will give that a try.