What's New in Activities - Mark all Read not working

For some time now, I have noticed that when I click on Mark All Read, the history APPEARS to have been cleared, but when I come back the next day (or even later on the same day) my last visit is listed as 2 days ago, or one day ago, or even on occasion 3 days ago, and the downloads that I have carried out are back again. Clicking on them reveals that I have indeed already downloaded them.
I have taken to clearing history multiple times, but that doesn't appear to stop this frustrating activity.
I wonder if it may be related to me using the feature around the time the server is clicking over to a new day (where ever it is) - I'm in Australia, so presumably there would not be many users clearing this list when I do.