I cannot find where to turn off lock screen notifications on a per app basis, you can either show all notification content, hide sensitive content, or don't show notifications at all in the lock screen preferences. This happens currently on my 6T, Pixel 2 did it when it got Pie also. I get notifications on the lockscreen and ambient display for everything unless I turn off notifications completely for that app. Used to be, at least in oreo on the pixel 2 I could change lock screen notifications on a per app basis.
Maybe I'm missing it, or not remembering right, but I'm pretty sure I could set apps to give me a silent notification only in the notification bar, not on the lock screen, aod or ambient display and no vibration or sound. Now its either they are on throughout all layers or none on Pie. Again, maybe I just haven't found it but I really liked that, you could prevent apps buzzing like crazy and lighting up your screen but they would still be there when you unlocked the phone.