Not sure if this is a 'bug' or not, but something I've been noticing a lot recently is that while I'm moving a Settler with an escort they'll just suddenly stop all of a sudden, seemingly for no reason.
I've noticed that they're actually stopping because an enemy unit is nearby, except that I can't see it. As an example, just now I was moving a stack with a Settler in it on a Go To mission, and they just stopped a few turns before they would have reached their destination, canceling the order in the process. I took one Musket out of the group and had him move towards the fog one tile southeast, and several tiles away was an enemy Greek stack of military units.
They shouldn't have stopped because of this stack there, because I couldn't see it and it wasn't within their line of sight at all, but they did anyway. During the testing phase earlier, in one of the mid-game revision updates, I noticed this as well. When moving a settler and two archers over to the Cotton hills spot they'd cancel their Go To order even though there were no enemies in sight. Enabling Debug mode to see the revealed map, there was a barb warrior in the fog where neither I or my units could see, but it caused them to stop and cancel their Go To order anyway.
Is this an intended feature or a side-effect of something else?