[Environment]
•Application: Adobe Illustrator 30.6
•Platform: macOS
•Language: Korean UI
•Text Type: Area Type
•Composer: Japanese Composer
•Language Options: East Asian Options enabled

[Summary]
While editing an Area Type text frame, several characters near the end of the text were modified. Immediately afterward, a portion of the text disappeared.
The text itself still exists and is selectable, but is no longer rendered correctly.
The issue is also reproduced in exported PDF files.
Creating outlines renders all missing text correctly.
Changing the Composer temporarily restores the missing text, but introduces different layout corruption (first-line indentation becomes incorrect).
Creating a brand-new Area Type frame and pasting the identical text completely resolves the issue.

[Workflow]
The document was created as follows:
Original document created in Adobe InDesign.
Exported as PDF.
Text copied from the PDF.
New Illustrator document created.
New Area Type text frames created manually in Illustrator.
Text pasted into the new Area Type frame.
No Illustrator document was converted from older versions.

[Steps to Reproduce]
Although the issue cannot currently be reproduced consistently, the following sequence produced the problem.
1. Create a new Area Type text frame.
2. Paste Korean text copied from a PDF exported from InDesign.
3. Edit several characters near the end of the paragraph.
4. Part of the text suddenly disappears.

[Expected Result]
•Text remains visible after editing.
•Paragraph composition remains unchanged except for edited characters.

[Actual Result]
•Part of the text disappears.
•Text object still contains all characters.
•No text overflow exists.
•Exported PDF also contains the missing text.
•Creating Outlines displays all missing text correctly.

[Investigation Performed]
The following tests were performed.
[Font substitution]
Changed the font to another Korean font.
[Result]
Issue remained identical.

[Text Overflow]
Verified that no Area Type overflow existed.
[Result]
No overflow.

[Reset Bounding Box]
Object → Transform → Reset Bounding Box
[Result]
No change.

[Clean Up]
Object → Path → Clean Up
[Result]
No change.

[Composer Change]
Changing the Composer temporarily restored the missing text.
However:
•first-line indentation became corrupted
•paragraph layout changed unexpectedly
•switching Composer again produced different rendering issues
This suggests recomposition inconsistencies rather than a paragraph formatting issue.

[New Area Type Frame]
Created a completely new Area Type frame.
Copied the identical text into the new frame.
[Result]
Everything rendered correctly.
The issue remained only in the original Area Type object.

[Additional Observations]
•The problem is not font-dependent.
•The problem is not caused by Area Type overflow.
•The text data itself is intact.
•Rendering becomes normal after Create Outlines.
•The issue appears to be tied to the original Area Type object.
•Recomposition triggered by Composer produces inconsistent layout results.

[Suspected Cause]
The issue appears to originate from the internal composition state of a specific Area Type object.
Possible areas to investigate:
•Area Type internal composition cache
•Japanese Composer recomposition
•Area Type rendering state after editing
•Korean text layout recomposition

[Files Available]
The following can be provided if necessary.
•Original AI file
•Screen recording
•Before/After screenshots
•PDF export demonstrating the issue

The issue was isolated through multiple troubleshooting steps, and the only reliable workaround found was recreating the Area Type frame. Since the text content, fonts, and paragraph settings remain identical, this appears to be related to the internal composition state of the original Area Type object rather than user formatting or font corruption.