I was having this issue after upgrading to iOS 13 too until I fixed it today. I have a Suunto Fitness 3 (software 2.8.24). I changed the settings on my iPhone to let messages display previews when the phone is unlocked. Before, I had this setting as ‘Never’.
My iOS is 13.1.3. Here’s what I did:
Go to Settings > Notifications > Messages
Under ‘Options’ go to Show Previews.
Change to ‘When Unlocked’.
Hope this helps.