1974 Townhome I did today. Original electrical panels. Found this when I checked out the main panel. That blue taped wire is the UFER ground wire. Attached at the foundation but never secured in the panel. Outlets in the dwelling showed grounded. Bonding wire for the gas and water was also flopping in the wind. Slab foundation. I can only suspect that since the ground wire from the UFER passes through the cabinet and was touching it there as a poor ground present. Needless to say I have called for an electrician on this one.
Sorry about the cocked picture can’t seem to get it corrected.