Imported Project Plan Not Saving


Hi - I'm importing an existing project from a .xml file which appears to load correctly with all the resources and dependencies copying across nicely. I click 'save' and everything looks great, however when I come back to the project plan later it's blank. I've tried it a couple of times and I've gone to the trouble of setting up alerts for if anything changes on the plan, so I'm confident that the plan is in good shape when it first populates into Smartsheet.

I've got around 80 projects to migrate so hopefully this is just something I've done wrong and can be easily corrected.