We construct an example to hopefully clarify some strange behavior in wiki frames.
Here we construct another example. It works when the page first loads. window.origin is defined in this case.
Clicking the reload button triggers a reload of the frame. window.origin is null in this case. We don't understand why origin would be null after reload. But the null origin causes a CORS error to prevent the graphviz-viewer.js from loading.
http://eric.dojo.fed.wiki/assets/pages/disappearing-frame-origin/frame-origin.html
We double-check our assumptions.
https://wiki-hacking.glitch.me/2021-08/frame-origins.html
HEIGHT 300
Frames in frames reveal that the surprise is that this works at all in the original page load. source 
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The original mystery was found in a frame aiming to use the <graphviz-viewer> within a frame.
When the page loads, a simple graphviz graph is drawn within the frame. But when we instruct the browser to reload only the frame, the graph is not drawn and we find CORS errors in the browser console.
We've copied the original frame item here. To test the behavior, try right-clicking (or two-finger clicking, or ctrl-clicking, as appropriate for your device) to summon a context menu & choose therein the "Reload Frame" command.
http://ward.dojo.fed.wiki/assets/pages/clickable-svg/test.html
pages/disappearing-frame-origin
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We ponder project 'Exact Codename' but have to check if our NDA has expired, before we can say more.