Do you have a NewsBlur Premium subscription? That sounds like a free account hitting the 3 stories/folder limits. I believe the Android app should have a banner that says that premium accounts are necessary to read by folder. I recently instituted the cap on the server side, and that may have broken things. If you see the banner when you try to read on the web, then that’s the issue.
I’ll make the change on Android right now so you see the banner.