I've tried three times to downgrade my wife's AT&T S5. It keeps failing in Odin. Here is the log:
<OSM> Enter CS for MD5..
<OSM> Check MD5.. Do not unplug the cable..
<OSM> Please wait..
<OSM> G900AUCU1ANCE_G900AATT1ANCE_G900AUCU1ANCE_HOME.tar.md5 is valid.
<OSM> Checking MD5 finished...