Your site's mermaid.maxSource option limits the total characters of Mermaid source a document draws, across all its diagrams. A diagram that would exceed the remaining budget shows its source as a code block with Copy instead. Shorten it or move it to another document.
The limit is a preset option, not part of the Markdown. If you own the site, choose the budget when you register the preset and pass its plugins to the linter too:
import comarkUi from "comark-ui/html";
import { lint } from "comark-linter";
const preset = comarkUi({ mermaid: { maxSource: 8000 } });
const issues = await lint(markdown, preset);Only diagrams that draw use the budget, so a later, shorter diagram can still fit after one shows its source. With no maxSource option, the preset does not limit the source length.