No one knows why your Mavic disconected nor what state it was in after it did .... it could have dropped into ATTI mode after the disconection which might explain why it did not RTH .... The point I'm trying to make here is once it disconnected it Would have been influenced by the wind. What was the wind speed and direction at the hight you were flying at on this day ??
And if you are flying above your set RTH hight the Mavic would not descend to the RTH hight at all it would stay at it's current hight and fly home in normal circumstances.