I have upgrade You track from 6.5 to 7.X to 2017.3. The usernames have been change to have an underscore and letters after them. eg carolrobertson has become carolrobertson_wU2q.
When I try to create a time tracker report. Not all the names are in the Work Author list and the ones that are have the underscore after the name. This then does not match to any of the existing issues, so the report doesn't pick any issues up.