iMessage filter for known senders keeps reverting to all messages on iPhone SE

I am filtering my iMessage to “known senders“ only. This worked very well well for about about one hour hour but then iMessages reverted back to all messages on my display. I returned the filters, click again on known senders, it seems successful but then an hour later it revert back to all messages; from both known and unknown senders. I don’t want to see messages from unknown senders.

[Re-Titled by Moderator]

Original Title: why does my iMessage filter for known senders continue to revert back to all messages? I want to remain on unknown senders continuously.