Several times I've seen my sovereign get stuck near water.  It's been when I've set a destination for it and the path take it near water.  It won't move then until I manually reset the detination away from the water.  I don't know if this is the same as your case or not, since as far as I can tell you're a bit farther away from the water than I was, but I guess it's a possibility.

It was the sovereign's territory, not foreign.

I have had one issue later today which was even weirder. Sovereign would not move, even when given a location manually. I had to manually take a couple of steps back and re-issue the move command. This was when sovereign had to move diagonally between two bodies of water (if that helps). It worked after moving him back and re-issuing the command.

I will try to reproduce tomorrow. Might be difficult though...

Maybe it's related with the "can't go there even if it looks you should do" bug. You konw, tje bug where you click on a tile next to the see, and in fact the tile isn't available.

I don't generally use this, but try selecting the unit and then hitting the "e" key.

Thanks tiefling!  I'll give it a go in the debugger and see what's up.