Thanks to @Tywyn who provided the initial password I was able to figure out why this happened. The installer uses the password to update the storage node setting in a way that is prone to a URL encoding issue. I have to admit I didn’t know base64 encoding can actually produce strings that can cause such a problem:
$ echo -n 'as~ja$j2niau83j2' | base64
YXN+amEkajJuaWF1ODNqMg==
The + character is then miss-interpreted by the PHP code as space character and therefore breaking the base64 decoding of that string.
I just pushed a fix to dev-branch in hope if this fixing all cases that special characters could cause in that part of the code.