Photoshop files much larger than usual.

I found a solution:
The script provided should strip the metadata in Photoshop just run the script before saving the files out. Adobe has no need to create artificial bugs.

function deleteDocumentAncestorsMetadata() {    
    whatApp = String(app.name); //String version of the app name    
    if(whatApp.search("Photoshop") > 0)  { //Check for photoshop specifically, or this will cause errors    
        //Function Scrubs Document Ancestors from Files    
        if(!documents.length) {   
            alert("There are no open documents. Please open a file to run this script.");   
            return;   
            }    
        if (ExternalObject.AdobeXMPScript == undefined) ExternalObject.AdobeXMPScript = new ExternalObject("lib:AdobeXMPScript");     
        var xmp = new XMPMeta( activeDocument.xmpMetadata.rawData);     
        // Begone foul Document Ancestors!    
        xmp.deleteProperty(XMPConst.NS_PHOTOSHOP, "DocumentAncestors");    
        app.activeDocument.xmpMetadata.rawData = xmp.serialize();    
        }    
}    
//Now run the function to remove the document ancestors    
deleteDocumentAncestorsMetadata();

But I could not understand the source of the problem.

The new document is created correctly. But when I copy a layer from a problem file into a new document, it also takes 62mb

essentially the same

is hardly the same as »the same« …

Drollery aside have you changed the File Handling Preferences?

Also different image content compresses differently well, so the difference you described does not seem shocking to me.