Canceling “Build Player”, during the “Mesh Data Optimization” step, causes Unity to crash. Please see the attached crash.dmp to Case 1168004. The project to reproduce this issue with is attached to a different report: Case 1108597.
I was actually creating a bug-report for this issue , recorded a video of the never-ending “Mesh data optimization” progressbar, then had enough and pressed “Cancel”:
The “Cancel” button then became disabled and Unity didn’t do anything for about 20 seconds or so. Then the “editor crash bug reporter” appeared.
I didn’t try to reproduce the crash again, but submitted just the report with attached crash.dmp file. Hopefully it helps you to fix it.