After upgrading to the latest version of the plugin, our existing checkboxes are now hidden..
They are showing in the HTML but with a visibility hidden..
I am suspecting it might be the new scrollbar script (?), but I am not sure. It is going to be updated for the upcoming release.
Until then, please turn off this option, it should resolve the problem: https://i.imgur.com/W6GkEO7.png