I've upgraded from RH 9 to RH19 and when opening the existing project initially it prompted me to save a back up copy (which I did) and then upgrade the one I am opening, which I also did. It seemed to go just fine; however, when I am in that project there is nothing there....none of the many, many topics that are contained in the original project.
I am not clear whether you mean you upgraded to 2019 Classic then 2019? If not, you should do that. Also make sure you update RoboHelp to Update 9 if not already installed.