Issue with Form submission (confirmation message does not appear)

I have been experiencing issues with my form submissions for some time now; there seems to be a glitch whereas the "success, your form has been submitted" message (that I type into the settings) does not appear when you hit the "submit" button. Instead, it just goes back to an empty form, thus making people think that it didn't go through, and then they submit again, and again... sometimes I'll get a dozen empty form fills too because I think they must keep hitting the submit button - this is what happens when I test it out myself anyway.

Can someone please help advise with this issue? Is it a bug? Is it my settings?

Thank you!