If I then redraw the whole diagram (from my model) using the same node positions, the lines are OK. This suggests that the nodes are not too close together. It shows that the GoDiagram line drawing algorithm can draw a reasonable line with the nodes this close together.
The problem occurs only if I have AvoidsNodes = true, but I don’t really want to turn that off.
Because the lines are OK when I redraw the whole diagram, I tried forcing the affected links (the ones connected to any node that is moved) to redraw:
link.AdjustingStyle = GoLinkAdjustingStyle.Calculate;
but this did not solve the problem.