Upgrading all the electrical outlets, switches, and most light fixtures in the house beginning with the outlets.
I test all the outlets prior and then again post replacement. One of the circuits had 6 outlets that all tested good. I replaced them then tested again. 4 of them indicate open ground. WTF! Start troubleshooting the cause and got it narrowed down to the one that is causing the problem.
The problem: When I removed the new oulet, their were 3 extra ground wires in the box along with the one hooked to the outlet. Upon further inspection, I found these wires weren't tied together thus causing the issue. Apparently, they were touching enough to give me a good read on the old sockets, but when I replaced the outlet it disturbed their "nesting" position enough to lose contact.
Problem solved.
Pro Tip: get on your knees and inspect each wire in every box so not to double the effort.