Hi,
Thank you for pointing out the performance issue of auto-fit operation with Comments. We have solved it in the new version v2.1.2, please try it. We have compared the generated files of your test program with Aspose.Cells 2.1.1.23 and 2.1.1.27 and found no difference between them. And, both generated files can be opened and closed fine here. Would you please try the new version and test the generated file again? If it still causes MS EXCEL crashed, please tell us more information such as the Excel version, the operations you did in MS EXCEL before closing it etc.
Thank you.