I just realized that my iPhone SE, iOS 12.3, isn't issuing the "ding" tone when texts are received. The Messages app shows a badge (small red circle) when a message arrives. The ring for a phone call works correctly.
The text tone sounds correctly in Settings > Sounds > Text Tone, Do Not Disturb is turned off, and Settings > Notifications > Messages is set to "Allow." I've restarted (soft and hard), and the Mute switch on the side of the case is in the up (sound allowed) position. Selecting another text tone has no effect, the different tone is also not issued.
What else might I try?