Instead of displaying the name of the person responsible for making a change to an item, it will sometimes show Unknown in the metadata comparison results table.

This can be caused when Salesforce does not return the full information for the Changed on / Changed by for some metadata items via the API. 

In these cases you’ll see Unknown as the Changed by value. This can typically be components of larger objects, such as fields on a custom object. Gearset shows these as discrete components that can be deployed, but Salesforce generally only returns the Changed information for the parent object.  

We are hoping that over time, Salesforce will improve the reporting of the API to include more information for these sub-components. As soon as it does, we will display that extra information.