Describe the Bug

We are having a problem with (initially) 25.12.4 and 25.12.5 when editing drawio diagrams.

The drawio-diagram attribute gets removed from the html in the page_revisions table and this results in the diagram not being able to be opened for editing again. The problem occurs when using the default settings for APP_CONTENT_FILTERING.

Steps to Reproduce

User 1:

Create a page
Add a Drawio diagram
Save the page
Edit the page again
Edit the diagram - OK
Save the page

User 2 with rights to edit the page opens the same page:

Edit the page
Tries to edit the diagram in Drawio but cannot double click.
Save the page.

At the point which user 2 saves the page, the drawio-diagram attribute disappears from the row in the page_revisions file and no-one can edit the diagram any more.

Expected Behaviour

Different users should be able to edit and update the drawio diagram.

Screenshots or Additional Context

If we set

APP_CONTENT_FILTERING="jhf"

the problem does not occur. However, this does not appear to be the recommended setting?

Browser Details

No response

Exact BookStack Version

25.12.5