Hey @markusvienna,
Thanks so much for getting back to us with that information! To be sure that I’m understanding – is the plugin not adding anyone to the connected MailChimp list at all, or is the success message simply being hidden?
That being said, when I mirrored your testing environment to the best of my ability (I was unable to test with that theme) the plugin still functioned normally on my end. However, when testing on your page I did see a few warnings pop up in the browser console, one of which can be seen here: https://cl.ly/471C3O0x2x2d – these warnings seem to indicate some sort of scripting conflict. For example, there are a few different jquery versions running on the page. I suggest taking a deeper look into this with your developer on staff to see what is causing those issues, as it does not seem to be related to a plugin conflict specifically.
Thanks – please feel free to reach back out at any time if you have other questions we can help out with!
Pearl