Lock-screen preference also affects notification

[Spike-from-NH]

When the setting "Lock screen notification visibility" is set to "Nothing", it also results in an empty notification in the windowshade and inhibits the medallion on the home-page icon. If you meant this setting to have all these effects, at least reword the prompt.

Observed on Samsung J3 with Android 9 and Samsung J7 with Android 8, Messenger 5.19.3.
Initially reported and misdiagnosed in #765.
Low priority; obvious workaround.