I've got a couple of Hidden fields where I'm setting the values with jQuery but the values don't come through in the submission.Data array.
I can see in the browser dev tools that it is set.
Your fields are Pre-defined hidden element blocks or custom hidden element blocks (inherit from HiddenElementBlockBase) ?
And how do you set those values, on page load or right before xhr request is sent ?
Sorry for the late reply, I had to reinstall everything on my laptop and we've been moving out of our house. :(
These were custom hidden element blocks updated during page load. I was able to workaround the issue by storing the value in a cookie and then using a FormElementBlock that reads the cookie.