Yes, when I re-opened VSCode, the preview pane reopened as well because I used it last time, but there was no content. I clicked on the "Dendron: Show Preview" button which made the preview pane fill with content but the Mermaid diagram rendered as literal text (as if the triple-tick enclosure rendered source code). Closing the preview pane completely and opening it by using "Dendron: Show Preview" fixed it.