Quick answer: Unity TextMeshPro silently truncating text past 16k characters? Mesh vertex limit hit - split into multiple TMP components or use the dynamic font asset's pageable mesh.
Chat log display tops out around 16k chars. Older messages disappear without an error.
Split into pages
Chunk text into 8k-char blocks; render each in its own TMP component. Layout container handles flow.
Or use UIToolkit Label
UI Toolkit's Label uses a different mesh strategy; doesn't hit the 16k wall as quickly.
Truncate visibly
If splitting is heavy, show 16k of recent text + 'load older' button. Most chat UIs don't need full history visible at once.
“TMP is one mesh. One mesh has vertex limits.”
If you ship chat or logs, plan for unbounded text. Pagination is the cheapest scalable answer.