Late for a Patrol

[Redmane]

It could be that your next assignment was a deployment rather than a patrol area. The map icon for patrol has binoculars in the star, the deployment icon has a flag. When approaching a deployment location the icon will grey out before you reach it, and you should receive a message updating your mission objectives. If none of this applies, then I'm not able to help further, sorry.

[TorpX]

What is the nature of the "deployment" mission? Just go there and sink stuff?

[fireftr18]

When you are assigned to a patrol, you get one of two options. I forget how they're worded in the orders. You can tell on the marker stars because one has a flag and the other a binoculars.
When you get the flag, all you have to do is arrive. When you get into the patrol zone, you'll get new orders that will say something like, "Sink enemy shipping."
When you get the binoculars, you need to stay inside the patrol zone for a certain amount of time. In stock, I think it's a 50nm radius. Mods change the radius. If you leave the patrol zone, the timer stops, then start over when you back in the zone.