A couple of years ago, while experimenting with SYLK files, I created a .slk file that caused Excel to crash.
When you create a text file with content “ID;;”, save it with extension .slk, then open it with Excel, Excel will crash.
Microsoft Security Response Center looked at my DoS PoC last year: the issue will not be fixed. It is a “Safe Crash”, Excel detects the invalid input and calls MsoForceAppExitIf to terminate the Excel process.
If you have Excel crashing with .slk files, then look at the first line. If you see something like “ID;;…”, know that the absence of characters between the semi-colons causes the crash. Add a letter, or remove a semi-colon, and that should fix the issue.