Applescript Slider widget disappears when using Javascript to return initial value

Describe the bug
When changing the script type for the initial value of an AppleScript slider from AppleScript to 'Real Javascript', the slider disappears from the Touch Bar completely. The script is returning a valid value, as this value can be seen in the editor

Affected input device (e.g. MacBook Trackpad, Magic Mouse/Trackpad, Touch Bar, etc.):
Touch Bar.

Device information:

  • Type of Mac: MacBook Pro (13-inch, M1, 2020)
  • macOS version: Big Sur 11.4
  • BetterTouchTool version: 3.562 (1704) - Issue is also present in version 3.562 (1702)

Additional information (e.g. StackTraces, related issues, screenshots, workarounds, etc.):
The slider does appear briefly, but disappears almost instantly.