@Galina6 Airbnb's notifications can be glitchy. I'll get notifications of some guest messages, but not others.
All I can suggest is to check more than one method of receiving those alerts-also try unchecking and then rechecking the SMS alerts box to see if that resets it. I have both SMS and email checked.
And contact customer service to see if their techies can do something about this. My SMS alerts stopped entirely a couple years ago, causing me to miss a booking request.
It took about a month and a half for them to fix the issue.