The ETC and ETC Costs amounts on a task with an expense resource assignment are blank on the time scale of an Open Workbench view. This is the case even when total ETC amounts are greater than 0.
Release: CODFSS99000-15.4.1-PPM SAAS FedRAMP-Sandbox-Small Environment
The ETC for expense resources will only show up correctly on the time scale if the Units/Format for the field is changed to Cost. This setting is found on the Formatting Options window that comes up when double clicking on the field on the View Definition window in Open Workbench.
Additionally, the costs will only show on the time scale if the resource has a valid rate for that time period.