Make an Appointment page keeps loading forever after making an appointment

I was not sure if it happens only to us but I received feedback from customers who describe the same problem; every time you make an appointment on our page (, you often do not get the pop up confirmation and a small round circle saying “wait” or “loading” continues to turn forever and nothing happens. This leaves everyone confused and uncertain whether the reservation was actually made and if we actually received the appointment. Email messages are sent though. As I said, we have tested this from several locations and received numerous messages from users regarding this.

I have a screen shot of what happens, it will stay like this forever

How can we fix that?