Cannot complete the "babylonian satrapy" mission tree

[The Magic B]

In my run with the Seleucids I am asked to own a province. I own every settled land in the province but there are 3 unhabittable desert tiles that remain. I cannot move pops to it, I cannot colonize it, yet it prevents me from completing the mission tree.... Does anyone have any ideas ? Because I seriously have none

 

[GabrielViolet]

There are small island in this province in persian gulf, it highlighted green on your first screenshot. It should be colonised to complete mission