Lost all lines, surfaces, and volumes after saving MSH file.
I'd been trying gmsh 2.3 for a few hours, wanting to create a mesh of a 3D scene for import into Elmer. After a lot of guess-and-check (because the Elmer documentation is uselessly cryptic) I did get Elmer to load the obstacles of the scene but there were no boundaries planes and no mesh volume. I had saved and restarted Gmsh several times during this process. Elmer seems to crash if the msh file has the "Save all entities" option ticked, so it is necessary to save all entities in one file, then save only physical groups to another file. I was also occasionally saving the geometry to a separate .geo file. The next time I loaded my .msh file, only the Points were there and all the lines and surfacesan had disappeared.
It was lucky I had a geo file as a backup, but still this should not happen.