Electrician came over at 9:30 PM tonight to replace the outlet. All fixed so far.
If it trips again, replace it again before getting into any extensive (and expensive) downstream troubleshooting.
Based on my past experience, the chances of getting a "bad" GFCI right out of the box is pretty high.
Brand names don't seem to matter, I get bad ones from Cooper, Harbor Freight, Leviton, you name it.
Also, once the newer ones have tripped a few times - - - even if it's just to test them - - - they go bad.
The older ones, like 15 or more years back, seem to hold up better, but, they still go bad if they get tripped a lot.
"Life is what happens to you while you're busy making other plans." - John Lennon