When running any kind of HR based workout (like DSW, or interval training), the initial screen has a heart rate gauge on top (with red/green/red zones to let me know if I am running too slow or fast).
However, upon navigating to this screen, the HR gauge doesn't show a 'needle' for cca 5 seconds. This means that if I switch to this screen during workout, I always have to wait 5 seconds before seeing if my tempo/HR is okay or not.
This delay seems completely like an UI issue, because the watch knows my actual heart rate every second - it just decides not to show it after navigating to the gauge screen.