hi, here is a project to reproduce the issue: https://github.com/hoangvannghia/ios18.4-crash FB: https://feedbackassistant.apple.com/feedback/16697708 thanks!

The stacktrace.

In my case it happens on a letter combination that produces a ligature. Updating the font setting (this is done by our font provider) can help to fix it. Removing the ligature feature also help to fix it. But I think there would be something wrong on iOS 18.4, please help to check it.