I have the same problem as well - it happens quite frequently. I am definitely not interacting in any way with any of the phantom accounts at the time, nor does taskmanager show anyone else logged in after an alert
I also get messages regularly saying that my webcam is trying to be accessed by either c:\windows\system32\taskhostw.exe or c:\windows\system32\devicecensus.exe
Full scan shows nothing suspicious on the machine.
Incidentally, my machine has 2 ESET phantom accounts- the standard "John" and also one randomly titled "rzjmporlfw". I previously looked into the second account and found threads saying that this was fine but was a bug in the phantom account creation. Deleting it just makes it get recreated again).
Perhaps a case for Eset Support?