I'm not sure I know exactly how to reproduce the bug either but I definitely also encountered this bug during my first campaign run at around 4/10. I had to restart the campaign from the beginning because I simply could not connect to the source tile anymore even though it was visually still present. I *think* what causes the bug to occur is putting a 3x3 zoom grid on top of a source and then deleting the source grid but I'd have to open the game again and double check.