Follow the below to resolve the issue:
Locate the matter name in the timesheet.
Open Central Console.
Filter for the the affected client.
In the left-hand menu, expand the Matter Console.
Select the relevant matter.
Click Action and select Unlock cloud timesheet entries.
Once completed, wait a few seconds and refresh the Cloud Timesheet. If the timesheet remains locked, allow a few minutes for the changes to apply and then try refreshing again.