When upgrading an outpost with the high tower to increase the area of control around, the border grow. If there are ressources on the tiles in the newly expended area the suggestion system event detect them.

BUT...

It is not possible to select these tiles to improve them, nor are they appearing in the possible build queue of associated city nearby. The fog of war also stay in this area as if the border expansion was not taken in account by some sub-routines in the game.

This bug is not systematic but quite frequent nevertheless. Reloading the game have it properly take in account the effective area though.