Facebook notifications not being cleared after being tapped on and read; seems to apply to certain friends/contacts. Why

(This is in the Android app)

Usually when I check Facebook I just go through my notifications; I rarely just scroll my newsfeed.

I’m sure part of this issue is familiar to many, namely that you tap on a notification, the relevant post appears and you read it, but when when you return to your notifications list, the notification is still highlighted.

What occurred to me recently is that at least some of the time, it’s notifications for posts by the same person or persons. I have one friend in particular with whom this seems to happen a lot. Eventually the highlight does go away, but it may take some time.

So what could I look at to fix this? Is there some setting I can change for this particular friend? I still want to keep the same friendship level and continue to receive notifications.