Links on your diagrams can either have a fixed direction (e.g. UP to DOWN, or LEFT to RIGHT) or be free to choose their own direction.
Links that are added by auto-connect have a fixed direction.
Links that you draw on yourself are free.
You can check this on a link by clicking the link and checking the direction icon. The one below is UP/DOWN:
Whereas this one is LEFT/RIGHT:
And this one is not fixed, as indicated by the wiggly arrow:
When the arrow is shown in red, this means that the direction is set, but it causes a contradiction on the diagram. That is, there is another link direction or layout which is overruling it:
The best approach is to move the elements of the diagram around to fix the contradictions.
In the case of a contradiction, usually, the link directions you set last will overrule earlier ones.