Trying to add a parameterized parameter to an already existing jenkins job (which already has a couple of parameterized parameters) does not work. When I click on "Add Parameter" drop-down menu and then choose "Choice" (or any other value), nothing happens besides the drop-down menu closing again.

When I last added a parameterized parameter a few weeks ago, it worked like a charm.

Deleting an already existing parameter also seems to work.