It turns out that the issue was related to platform encryption. If the new fields are Encrypted with Case Insensitive Deterministic encryption, Salesforce stores a lowercase duplicate of the field behind the scenes.
The first lwc that is encountered in a directory is considered the containing directory for all LWC components. Since you named it /lwc/internal/lwc/callbackIdRetriever, the system thinks you're trying to declare a component called internal. All of the source in those directories will be collapsed into a single folder for deployment, which means that any &...
LWC, in particular, are quite restrictive in their structure. Salesforce DX Project Structure and Source Format
Lightning web components must reside in a directory named lwc under
Even with the above restriction, you could define multiple package directories to have different lwc folders, but you can't have subfolders within lwc.
The problem is that you have both an Aura and LWC component with the same name. This is not allowed. You will want to delete or rename one of those components from the metadata files, presumably the Aura version. This may require some other refactoring of the code.