The following odd behavior did not happen until UE 5.2, but happens in the latest UE 5.3.
When the "Grid" show flag is disabled in the Level Editor Viewport, all billboard sprites and volume outlines also disappear from the view.
Interestingly, while any actor is selected in the scene (even an actor that does not include a billboard or volume component), everything appears normally (each item according to its own show flag). This also happens while the show flag "Show – Advanced – Shadow Frustums". But if no actors are selected and both "grid" and "shadow frustums" show flags are disabled, then the billboard sprites and volume outlines disappear again.
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-199942 in the post.