no idea, you're not like in a mission or something. do random encounters hide the mission icons?
maybe try killing yourself and see if it resets.
It's like that for all characters though(?), might be a glitch
EDIT: quick google, this came up GTA V – Can’t Trigger the Last Part of the Merryweather HeistIn the Merryweather Heist mission, you may not trigger the final part of the Port of LS Heist. This part may be lock; you must complete other missions as other characters such as The Long Stretch, Hood Safari, and the third FIB mission.
To complete the third FIB mission, you need to receive a phone call while playing as Trevor or Michael. Switch to those characters and make sure your in-game phone is on.