This issue is actually a memory crash, which can actually happen when there are lots of shape variants in a design, as they blow the maximum amount of kerning pairs (around 12k).
To mitigate this issue, you will need to apply the Smart Kerning feature manually on fewer characters:
- You must first use Reload Extension from the top-right tray icon or by restarting Illustrator (a computer reboot can also help if you've been working for long days):
- Then use the Smart feature in the Advanced > Spacing view if you want to automatically set the side bearings values
- And in the Kerning view, click Smart, but pick only a subset of characters, like just the Uppercase and Lowercase:
- You can alternatively apply it to an arbitrary set of glyphs (you can view them all when loading a new font in the Live Preview, and paste them in the Kerning preview to force Smart calculations on that text selection):