When reaching 100% while conducting a Lightmass Build with many objects at a HIGH or PRODUCTION level, and the build is finalizing, chances of a crash at the end of a build are higher. To reduce the odds of a crash, I have taken two steps that significantly reduced crashes at the end of the build.
First - Disable “Use Less CPU when in Background”. This option is located under Edit > Editor Preferences".
Second - Set Realtime “Off” or CTRL + R.
If the user does not have these options set during the light build, it would be nice if the system automatically sets these parameters once the light build is at 99.9% done, then automatically restores the settings once the finalized light building is completed.