Pan example (on Options page) error

The Pan example on https://sonic-pi.mehackit.org/exercises/en/03-tweak-the-sounds/02-synth-options.html doesn't work for me. The first time it runs, the sample sounds suppressed:

{run: 49, time: 0.0}
 ├─ synth :beep, {note: 36.0, amp: 0.5, pan: -1}
 ├─ synth :beep, {note: 36.0, amp: 0.5, pan: 0}
 ├─ synth :beep, {note: 36.0, amp: 0.5, pan: 1}
 └─ sample "/Applications/Sonic Pi.app/Contents/Resources/etc/samples",
             "drum_cymbal_closed.flac", {pan: 0.3501}

The second time, it sounds the same but the third time, the sound is clear but the pan isn't randomized:

{run: 51, time: 0.0}
 ├─ synth :beep, {note: 36.0, amp: 0.5, pan: -1}
 ├─ synth :beep, {note: 36.0, amp: 0.5, pan: 0}
 ├─ synth :beep, {note: 36.0, amp: 0.5, pan: 1}
 └─ sample "/Applications/Sonic Pi.app/Contents/Resources/etc/samples",
             "drum_cymbal_closed.flac", {pan: 0.3501}

Should also mention that I'm on OS X 11.2.2, and Sonic Pi 3.3.1.