Changing url of Git submodule fails

I have one submodule inside a project which I would also like to push automatically to staging. Now I made apropriate changes to the hook and also changed the authentication method from password to certificate of the submodule.

Unfortunatelly git refuses to make the change of the authentication method, despite the already changed url of the origin:

remote: /home/git/staging.git
remote: Cloning into 'MEW'...
remote: fatal: could not read Password for '': No such device or address
remote: Clone of '' into submodule path 'MEW' failed

node1:/home/www/demo/MEW$ git remote -v
origin (fetch)

cat .git/config

[submodule "MEW"]
     url =

Is this a bug or do I need to change something else to make the change happen? Thank you in advance for any help.

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