I did try the "restore device" but nothing actually happens (like there are no links). I'm wondering if because I tried to do a device restore on the defective keypad (which failed), and then tried the replace with the new keypad, somehow the new one copied over corrupted links or maybe there were no links to copy?
As for line noise, seems unlikely as I have dozens of Insteon devices in the house and they've been pretty solid for years, but I guess anything is possible.