POST serverconnect on iOS

I have a straightforward FORM that is submitted in a FLOW component.

It works fine in the browser and on Android, but somehow the Serverconnect is not submitted on iOS 12 (the Serverconnect actions outside of the form work fine and the flow actions also).

Tried debugging with a connected phone in Safari, but when I run the flow, no error is shown in either console or network tab (or any of the other tabs).

Any ideas?