No Mermaid previews on post edit

[Reinmar]

Try to edit this post. See that there's no mermaid preview.

flowchart TB
A --> B
B --> C
C --> A

[Reinmar]

This is what I see:

[mateuszzagorski]

I've looked at it briefly and while doing so I've found another problem:

1. Follow the steps you've mentioned -> Try to edit the post - you'll see only the code, but not the mermaid preview.
2. Click on the "cancel" button.
3. Try editing the post again - you should not see anything - the code vanished.

If you cancel the editing, the mermaid should be visible normally. But only refreshing the page brings back the code for me when you try to edit once more.