if you are having issues creating FBA shipments today, you are not the only one. There is a significant technical issue impacting the entire US Amazon marketplace, which causes all Send to Amazon workflows to get stuck in the half-way to completion with an error message stating:
Something has gone wrong. Try refreshing the page. If that does not
work, please delete the workflow and create a new one.
After consulting the Seller Support, I have been told that they are working on it so that it can be fixed as soon as possible.