Explanation & Solution of Issue
ETC has identified this cause as a bug in the Clonezilla software which will be fixed in a future version on both products. Certain monitors seem to not like the display resolution that Clonezilla switches to during the image process, and those monitors handle this by not displaying anything at all. Fortunately the image process continues in the background if left untouched, and the unit powers off when completed so it's easy to tell when it's done. Additionally trying a different monitor may work, as not all monitors are susceptible to this issue.