Some side ops (missions) in the MGSV:TPP stay highlighted with a dot on the left side, even after the mission was done. What does that means?
Basically a white/yellow (with yellow being "more important" kind) dot on the left side of a mission means it has just appeared (same goes to tapes/staff/etc.).
Considering you have already finished that mission I would classify this as a minor glitch/bug.
Another possibility is that you haven't (for example) extracted all possible valuable targets from given mission and the game simply notifies you of this fact.