Salesforce Sandbox: 'Maximum Logins Exceeded' Error After Full Sandbox Refresh

Option 1: Change the Profile of the Affected User and Then Assign It Back

1. Navigate to Setup and type User into the Quick Find box.
2. Click Users:
   1. In Lightning Experience: Users | Users
   2. In Salesforce Classic: Manage Users | Users
3. In the right-hand column of the user information, change the profile from its current setting to any other profile.
4. Click Save.
5. Click Edit on the same user.
6. Assign the original profile back to the user.
7. Click Save.

Option 2: Clone the Profile of the Affected User and Assign It to the User

1. Navigate to Setup and type User into the Quick Find box.
2. Click Users:
   1. In Lightning Experience: Users | Users
   2. In Salesforce Classic: Manage Users | Users
3. Click on the impacted user.
4. In the right-hand column, click their Profile.
5. Click Clone.
6. Enter a new profile name.
7. Click Save.
8. Return to Users.
9. Click Edit next to the user's name.
10. Assign the newly created profile.
11. Click Save. 

After completing either option, try to reset the password again.