Bookmarks do not jump to the right place in HTML code in a text element on a hub page.
The right place is several lines further up and out of sight.
Sometimes it works correctly when I first arrive at the page, but not for subsequent links.
See this file that I have on ArcGIS Online: https://twdb-flood-planning-resources-twdb.hub.arcgis.com/pages/test_bookmarks#h6
You can change the 6 (in the URL) to any of the heading numbers to experiment with jumping around the document.
I will also attach the html code from the text element. You would need to paste it from this file into the code view of a text element on a hub page to replicate.
I have the problem in both Chrome and Edge.