For me also on the Chromecast app and the android app, subtitles will progressively get more and more and more out if sync until it is like a 2-3 second difference then holds there.
I know that the subtitles I got for the episodes are in sync and on the web app they are in sync.
Does the problem remain if you skip back 30 seconds or more? I’ve found in the past with other software that doing so can resolve some of these issues. Is it a particular client you’re using?