I noticed a bug that occurs with WordPress and the Twenty Twenty Two theme I’m using in conjunction with the BibSonomy/PUMA CSL plugin, which (to be fair) hasn’t been tested with 5.9.1 yet.
If the plugin is enabled, the html link references to the site icon
<link rel="icon" href="https://sdoerner.de/wp-content/uploads/2022/03/cropped-sdoerner_logo_test-32x32.png" sizes="32x32">move from html <head> (where they should be) to html <body>. I think this behavior is kind of odd and I would expect that linking the icons should be done before and independent from plugin scripts within WordPress.
This causes many browsers to not accept or follow the link to the site icon, thereby it is not showing as expected. Chrome for example then desperately tries to get /favicon.ico and does not care about the links (because they are now in <body>).
I’m not sure whether this is a WordPress bug or the plugin’s bug, but I found several mentions of these kind of bugs about WordPress site icons when I was googling. So if you found your way here because you had similar issues, one could think about filing a bug report.