Modified By Column on Period Checklist does not show the user who last locked/unlocked a task for a subsidiary.

Setup > Accounting > Manage Accounting Periods:

The Modified By column will show the user who changed the status of that field.

 

For example:

If user A is the one who first locked the Lock A/R task for a particular subsidiary it will show on the system notes of the accounting period that the status of the field was changed from Unlocked to In Progress.

If user B locks the Lock A/R task for another subsidiary but there are still unlocked subsidiaries, the period will still have a status of In Progress for Lock A/R task and the Modified By field will still show user A since the status did not change.

 

The Modified By field will only change if all the subsidiaries have been locked (or changed back to unlocked).