Keywords fail to write to file

Try resetting your preferences.

Troubleshoot Adobe Bridge for freezes and performance issues

If that doesn't work, test with this script to see what happens. Save it in a text editor as a PLAIN TEXT file (not RTF) with file extension .jsx. Open Preferences->Startup Scripts and click the button to reveal the scripts folder. Drag the .jsx file in and relaunch Bridge. Run that script and see if all selected files have keywords added.

#target bridge

if(BridgeTalk.appName == 'bridge'){

    VT = MenuElement.create('command', 'Keyword Test', 'at the end of Tools');

    }

VT.onSelect = function(){

    keyTest();

    }

function keyTest(){

    var thumbs = app.document.selections;

    var keys = ['Test', 'HTest|Testing', ''];

    if(xmpLib == undefined){

        if(Folder.fs == 'Windows'){

            var pathToLib = Folder.startup.fsName + '/AdobeXMPScript.dll';

            }

        else{

            var pathToLib = Folder.startup.fsName + '/AdobeXMPScript.framework';

            }

        var libfile = new File(pathToLib);

        var xmpLib = new ExternalObject('lib:' + pathToLib);

        }

    try{

        app.synchronousMode = true;

        for(var a in thumbs){

            if(thumbs.hasMetadata){

                for(var b = 0; b < 2; b++){

                    var md = thumbs.metadata;

                    var xmp = new XMPMeta(md.serialize());

                    xmp.appendArrayItem(XMPConst.NS_DC, 'subject', keys, 0,XMPConst.PROP_IS_ARRAY);

                    xmp.appendArrayItem('http://ns.adobe.com/lightroom/1.0/', 'hierarchicalSubject', keys, 0, XMPConst.PROP_IS_ARRAY);

                    var updatedPacket = xmp.serialize(XMPConst.SERIALIZE_OMIT_PACKET_WRAPPER | XMPConst.SERIALIZE_USE_COMPACT_FORMAT);

                    thumbs.metadata = new Metadata(updatedPacket);

                    }

                }

            }

        app.synchronousMode = false;

        }

    catch(e){

        alert(e + e.line);

        }

    }