@Sue1527 There can often be glitches in receiving alerts. My text alerts stopped altogether a couple of years ago and it took Airbnb a month and a half, first to acknowledge that it was a tech glitch on their end, and then to fix it.
Sometimes I get alerts for some messages and not for others.
You should check off a couple of different notification options, so if one fails, hopefully the other still works, and get in the habit of checking your message Inbox at least once every 12 hours, so you don't miss anything.