Google OAuth login redirects to image file

I am trying to set up Google OAuth login, using Ansible to create the grafana.ini file and deploy to my Grafana instance. It sits behind a reverse proxy and my root_url is set. Everything works fine, except that upon login my browser navigates to and loads a 404 page. The GET call to /login/public/img/fav32.png returns 200 OK and I can look at the image in my Chrome dev tools. I can navigate away from the 404 page and use the rest of the site without issue. Upon closing the window and reopening it, remaining logged in, I am immediately navigated to again and served the same 404 page.

At this point I am left with just an inconvenience because there is a simple workaround, but I would love to know how to solve this. I suspect that the callback URL is incorrect but other than generating new OAuth credentials I don’t know what to try.

New discovery: This happens on Chrome 97.0.4692.71 but it doesn’t happen on Firefox 96.0.1 or Safari 15.2 (17612. - latest versions as of 2022-01-14.