On standalone Windows computers or those in a Windows workgroup, when you change the username, you are only changing the cosmetic name that appears on the login tile. The underlying user ID stays the same. ActivTrak reports activity associated with the actual user ID.
To help manage this issue, ActivTrak provides support for user name aliases. After an ActivTrak alias has been assigned, the alias will appear in place of the user name on all ActivTrak reports. Go to Settings/Alias to assign or edit aliases.
For more background information on Windows user IDs:
This article will explain how to use Aliases in greater detail.