Internal error after Slider added to Experiment

OS: Mac (10.14.6)
PsychoPy version: v2020.2.10
Standard Standalone? (y/n) If not then what?:

I ran a pretty simple experiment in Builder and online (worked great in both but because the Rating component isn’t supported in JS, I added a Slider in Builder. After adding this, the whole thing stopped working and I got an internal error (see below)

What did you try to make it work?: I tried disabling the Slider component and then removing it altogether.

What specifically went wrong when you tried that?:
Traceback (most recent call last):
File “/Applications/”, line 1062, in runFile
File “/Applications/”, line 94, in addTask
File “/Applications/”, line 691, in addTask
File “/Applications/”, line 2854, in _ListCtrl_Select
wx._core.wxAssertionError: C++ assertion “”litem >= 0 && (size_t)litem < GetItemCount()”” failed at /Users/robind/projects/bb2/dist-osx-py36/build/ext/wxWidgets/src/generic/listctrl.cpp(3466) in SetItemState(): invalid list ctrl item index in SetItem