Just been watching the WSB practise coverage from Australia that was on overnight. And as before last year the app on my Chromecast dongle is not marking content as watched. Looking at the app on my phone and on my tablet and they are showing it as played. 🙄
With my programmer's hat on I am guessing that as well as there being a Play Point variable used to record the current play point which is used by the Resume option there is a related Display Play Point variable used by the app interface to draw the progress bar on the icon and it is that which is not being updated on the Chromecast version of the app.
Just an update: Noticed this weekend that while watching MotoGP that the progress bar is being shown in the Continue Watching screen but not in the MotoGP screen. And looking further down see that the same was true for World Superbikes last weekend. Hope that snippet of info helps sort it out. Mean time I will be making more use of the Continue Watching screen which will be especially useful for the British Superbikes coverage which gets shown as one all afternoon programme and which I tend to watch in two or three or more viewing sessions.