Is there something that I'm missing or is this a bug?
Do you have any of the captured traces checked in the Captured Data Sources list?
In the Display tab of the Controls drawer (at the bottom of the window), is the Draw column checked for the captured traces you are trying to display? Is the vertical scale selection appropriate for the data?
In this case, a screenshot of the Oscilloscope tool in the re-opened project could be helpful, so we can see what you are seeing.
Thanks,
Ben