I'm using an LG Stylo 3 Plus. I don't have the option to "preview messages" in my message app settings. I've also tried several different messaging apps. Any other ideas?
I found the solution! This bug is affecting all smartphones with face detection. By default, android disabled the preview of messages on lock screen while the face detection is turned on. It's understandable since when you lift your phone and it detects your face, it automatically directs you to the source of the notification.
What I did to my Huawei P20 Pro:
1. I set my lock screen notifications to "Display"
2. I deleted my face data.
3. Tried sending myself a message and right away pressing the standby button to check if there's a preview and voila! The preview is enabled.
4. I enabled my face detection again to see if it will remove the preview but i didn't.
5. Try switching the face detection option to "slide to unlock" if you just want to check the preview and don't want to unlock your phone totally.
I hope this helps!