I have the “Days of unreads” option marked as “Mark stories as read after“ 1 day.
However, I have multiple feeds older than 1 day that have stories marked as unread.
I thought the problem was only with newsletters I redirect to Newsblur, but it also happens with feeds added directly through Newsblur.
Are you a premium archive subscriber? You’ll need to be in order to set how many days back stories are marked unread. If so, post a screenshot of what you’re changing.
There are three possibilities I think of where you’re looking, which is why I want a screenshot.
Hey Samuel, thanks for the fast reply.
My bad, my subscription is regular premium (not archive), I forgot I don’t have access to this feature.
Doing it manually from here works:
I know it probably is overkill, but maybe it would be good to grey out the option in the menu to reinforce it is a premium archive feature. Here:
Note: looking forward to subscribe to premium archive in the future after I finish my PhD and get a job 
