Audio trouble on iPad

Got a course we've had for some time, first published in Lectora 16 and active in our LMS for a couple years from Lectora 17. A few minor revisions to the course, made in the same version of Lectora, have caused the audio to stop working a few slides in when running on an iOS.

Audio on the first two slides plays as expected, and the Next button lights up when the clips are done. Audio on the third slide does not play at all -- but only on iOS. It's fine on every other device we try.

All the audio cuts in the course are MP3. All are set to auto start. The controller display is set to None for all of them.

I tried republishing in L18.2.3; no change. I noticed that the first two slides had audio cuts with one-word filenames while the third had a longer filename with a space and a hyphen, so I replaced that cut with a one-word filename; no change. I don't know what else to try.

Anybody got a suggestion?