Something has changed with the update from 2.4.20 to 2.5.4 in terms of lazy loading.
I have integrated a Google Adsense ad below every 5th post (data-ad-format="auto"). Previously, the ad was loaded using lazy loading ("Refresh every 0 seconds"). This is no longer possible. As a result, the side anchor no longer work properly. So if you click on the first unread post, you initially get to the right position. But then the upper (not visible) ads on the page load, and the page shifts and you are no longer on the right position (the first unread post). This is very annoying and the first visitors are already complaining about it.
As I said: I didn't have these problems before the update to 2.5.4. The Google AdSense code is unchanged and so are all other ad settings. Could you please check this again?