Thanks Bruce good idea. I went over yesterday and checked all sw. and plug connection.
Checked voltage at panel 255v. A-B 127to N. Maybe a fluckuation triggering AFCI?
It may be days before any tripping.
When I was checking connections, I drew a visable-audible arc several times but AFCI didn't trip. I've experienced this on other houses I've wired, but without the problems of this house.