Hi Markus.
Markus Does anyone know what happened there?
Yes, the URI fields has been changed and now they can handle languages.
If you want to change the URI field definition to back to previous configuration you can perform the change into the ontology.
1 Login as super-administrator and select the field

2 in inspector click to edit the field definition.

3 Change the translatable definition to No and apply the change.

You will return to previous definition and you will able to export.
But update the version! the URI fields has been change to manage the labels in a common list and definitions. So is important to mantain your installation updated. (in the update the translatable will change to be coherent with the new situation)
I hope is clear.
Best