message notification

If the only problem is the number of messages appearing on the Messages app icon (the number is called a Badge), then do this:

Go to Settings > Notifications > Messages, and turn on Badges (and any other settings you need turned on).

If ALL notifications are missing for Messages (a known issue for some users), go to this post and follow the instructions to fix it:

Message Notifications - Apple Community

With the limited information that you have provided, I would say maybe they are being read on other devices logged in with the same Apple ID.