I'm guessing the affected recording was still in RAM while working on the project, but FL thought it was saved, and didn't save it again while working on the project. It'd be better if there were more graceful handling of the disk being full (no errors are given), including saving the full recording if it didn't save successfully the first time, or if FL prompted to export data files before exiting project if they're not saved properly etc.
At least its prompted me to finally install the new SSD that I've had sat on my desk for a month, so I shouldn't run into this issue for another 350GB or so
