You don't say what device you have but the 2 other threads you posted with the same subject are in the Droid Turbo forum so I'll go with that. Side note, posting a single new thread will help the people helping you so that all the suggestions are in one place.
The Turbo will have 2 options for lock-screen display, Moto Display and Android's Ambient Display. Which are you using?
For Moto Display, make sure the app didn't get turned off in the Moto Display options. I don't recall the path (I've since moved to a Nexus 6P) but when I had my Moto X this would happen from time to time and I had to go in and re-enable the app for Moto Display.
For Ambient Display, I haven't found the options for individual apps to display there or not, the only options I've seen were for full details or limited details on the full-color lock-screen display (under security I believe).