https://docs.opendatakit.org/form-update/ describes the kinds of changes that can be made.
There were recently big changes to the XLSForm converter that may result in incompatible converted form definitions. You can read more about what that would look like and how to troubleshoot at Cannot update form using XLSForm Online v.2.x. One quick thing to try is to add a name field to your settings sheet matching the filename and see if that fixes the problem. If not, you can also try the v1.x converter.