Had the same crash but for me it was for all .md files. Cursor would freeze when opened in the editor, but preview works fine.
Checked the logs (~/Library/Application Support/Cursor/logs/ → main.log) and found the breadcrumbs bar at the top of the editor gets stuck in an infinite loop trying to parse the Markdown headings.
Fix: Open Settings → search “breadcrumbs” → turn off Breadcrumbs: Enabled. File opens fine after that.