Oh weird. It isn’t actually anything to do with the theme.
On both themes it seems to work fine on load, but as soon as you change tabs it makes a GET call to update the favicon from:
https://forum.sfcu.com.au/favicon/proxied?https://forum.sfcu.com.au/uploads/default/optimized/1X/1c3e15c01aa86d6e49b8c8037b408aaa2058d4ba_2_32x32.png
And this seems to return a generic bubble irrespective of the query string (after the “?”).