The Map does not update as often as the mini-map. Green/yellow dots on the main map may persist after the avatar has left the area.
But...TWO DAYS of persistence?
If so, that might explain why the avatar still shows as being on my parcel.
I did load the 1.23 last night, and so was able to get the avatar name. It was registered three days before I first noticed it on my parcel...so the absence of Profile pic and picks might be due to the account being new. Or of course it might be a bot.
Also, in regards to the above and below indicators. Avatars over 2000 meters in the air will show as below you on the mini-map. Tested, repeatable, known bug.
This has remained a full, round dot in the days it's been there. Last night I flight-feathered up to 3500m...no sign of it.
Weird...
...There IS no way an avatar could be invisible to even the Highlight Transparency viewer toggle, is there!?!?!