Hi @mvaldes,
this has nothing to do with the settings in the Advanced tab. We introduced a new variable type for paths for the new reader nodes, so you would need to convert your string variables to such path variables using the String to Path (Variable) node, see also this post.
Where do you have these variables actually from? The variable names let me assume you are using the legacy File Upload node. If so, you can exchange it with the File Upload Widget node which outputs a path flow variable.
Best,
Simon