I’m able to reproduce this somewhat consistently in projects with Perforce source control. Since I’m using assembla, sessions don’t persist for more than 12 hours. If I open up an asset in UE4, modify and save it, then connect to source control and try to save it again, I get the “cannot be saved / partially loaded” message. only way to resolve this is to restart editor, discarding any changes. It appears that this only happens when I forget to immediately connect to source control upon opening a project.