I add PayPal info, it says it's saved, but then it's... not... I don't know how else to explain it.
I've disabled everything else and tried the 2016 theme. I have tried on another host.
Here is a little screen video that shows what happens. I will point out that I have a couple of threads going right now because I think there is a core issue with the way WPMU plugins handle ajax calls or something. Maybe there's a non-ajax version floating around that we could try? I doubt it, but I certainly don't mind having to click a 'save' button if it means the site will work.
Here's that video: