I was cleaning up a pretty dense design with 4 layers and started seeing a floating copper warning. I had manually re-routed some traces after auto-layout failed to catch some very close traces. Bottom Copper layer. Selecting the trace moved the position of the view but centered in on an empty area. I was able to select the 2 traces by clicking around. As you can see there is a copper pour cavity surrounding them. Right click menu > Delete caused the entire design to be deleted...
I do not have repro steps as I have made hundreds of manual tweaks and I'm not sure when this issue occurred.