HTML notifications don't seem to work with waitress

[matt-sd-watson]

I am using Waitress in my Shiny app with the following start code:

new_waitress <- Waitress$new(theme = "overlay-percent", infinite = TRUE)
new_waitress$start(h3("Generating panel"))

So I would expect to see 'generaing panel' in my waitress progress bar.

However, when the app is running, the following screen is shown and doesn't change until I call new_waitress$close(), so it is basically frozen on 1% progress:

Just curious if I am calling any functions or variables incorrectly here.