This is expected behavior. You can set the name column on the settings sheet to "host" if you want to change this behavior.
pyxform has historically set the form id and the root node in the XML to the filename. The change we've made is that the root node is now set to /data/, unless you specify a different name in the XLSForm. There is no change to the form ID behavior.
XLSForm Online v1.x
A form named my-form.xlsx with no custom id or custom name:
root node: /my-form/
form id: my-form
XLSForm Online v2.x
A form named my-form.xlsx with no custom id or custom name:
root node: /data/
form id: my-form
A form named my-form.xlsx with form_id set to foo
root node: /data/
form id: foo
A form named my-form.xlsx with name set to bar
root node: /bar/
form id: my-form
A form named my-form.xlsx with form_id set to foo and name set to bar