It's happening even if I haven't played in hours, days, and it also happens to others on our server but yet we are not connected more than once ever.
I've only noticed this since the latest patch. Even if I reboot system and log in for first time, it picks and chooses when it want to add the _2 to the name.
When even checking the names in the list you'll only see the 1 name but it will have the _2 on it.
I can even disconnect from server and rejoin seconds later and sometimes the _2 is gone.