OMG, I found it and once I did it is so logical!
I thought it might have been a bug introduced in rc of live_view, so I created a test app with 0.20.17. I created the hook added 2 pages with just a button that put_flash and push_navigate, immediately I noticed that upon clicking the flash would close after 5 seonds - great - but I also got
[debug] warning: undefined handle_info in TestHookWeb.Page2Live. Unhandled message: {:close_flash, "info"}
This decided me to try and return {:halt, ...} from info/2 and that fixed it!
Returning {:cont, ...} made live_view continue the event where it failed because I have an handle_info/2 but not for that event.
