well, this exact bug occured in my game as france!
i rushed to get some tradespots in the trade theatres and all of a sudden, when i tried to reinforce one of those tradefleet with 2 more indiaman, the trade income stopped to flow from that point and the reinforcing fleet was not movable anymore.
i could, however, move the single ship that was on the spot before and move it back in would yield 1 ship income, the other 2 ships were lost in oblivion i guess ...
happens near the province of New York often too, when you violently remove an occupying fleet from your port near there, it just sits near the coast and is not attackable or otherwise interaktive ...
strange thing, CA should look into i guess ...