If you see Protection is off on the Security tab, or the banner "1krBlocker isn’t your SMS app, so new messages aren’t checked." in Messages, another app has become your SMS app. Until you switch back, new messages aren't checked.
To fix it: tap Turn on on the banner (or on the Security tab) and choose 1krBlocker when Android asks which app should be your SMS app.
Why it happens:
- You (or a phone update) chose another app as the default SMS app, for example by opening Google Messages and accepting its "set as default" prompt.
- Some phones reset the default apps after a system update or a backup restore.
What about messages that arrived meanwhile? They went to the other app and weren't checked by 1krBlocker. To check them, open Settings → Scan my existing messages: it adds risk labels to the last 90 days of messages (nothing is moved).
If you meant to switch away from 1krBlocker, see "Switching back to another SMS app".