@juliaweist Thanks so much for getting back to me! Took some doing but got my issue resolved - thumbnails not showing for uploaded media on new records. Double checked my GraphicsMagick installation which proved to be the culprit. I reinstalled it from source using the option to enable jpeg processing which the previous install did not have strangely, ./configure --enable-shared --with-jpeg. Then made sure the path to the gm executable in my setup (Centos 6) was set properly in app/conf/external_applications.conf. Works great now!