Services selection issue

There is a problem with the onchange js function.
When I select more than one service, and then I deselect one of them, it switches between checked and unchecked for a bit, confusing the person who is selecting the services.

I made a video about the issue with the plugin so you can see with your eyes:
Link video

I need help, please, I’m working in production stage.
Thanks in advance. Gianluca.