Orchestrator API filter got wrong result

Hi, I’m using odata/Processes?$filter=Published gt 2019-08-15T00:00:00Z to get all the processes published after 2019-08-15, but the result is empty. However, if I change gt to lt, it will get all processes from Orchestrator, making this filter condition useless. My testing Orchestrator is 2018.4. But if I do the same thing on Orchestrator 2019.4, I can get the correct results. Is this a bug for Orchestrator 2018.4?