I'll try and find it. It was some time ago though.
EDIT: Found it, luckily, it escaped my replay purge. By a hair too, literally the first replays that didn't get deleted.
#5196596, around 19 minutes. It seems they are the ones going around to the right, if you engage them BEFORE they reach the right unexplored side, they will still run there. Maybe they lost radar coverage so they disengaged and continued their patrol?