Keynote song file stops playing at slide 44 before end of song

Keynote 13.2 (7038.0.87): I used the "Play Across Slides" option on the first slide then copied the audio object (m4a file) and pasted that onto every slide in the presentation (so, it's the same setting across all slides). Then I used the "record slideshow" option of playing it, to record the slide changes. The song audio stops playing at Slide 44 of a 51-slideshow, in which the song will play through to the end. I've tried re-recording the slideshow multiple times, and the audio stops at the transition from Slide 44 to Slide 45.

I've recorded a number of slideshows on Keynote and never encountered this before. Is there a limit to the number of slides Keynote will play across?