In my logical diagram and its subviews, a few of the lines (maybe 10%) representing relations aren't appearing between the entities. The relations exist and appear to be defined just as the ones that do appear. In "Show/Hide Relationships", they're flagged as selected, and I've tried clicking them off and on but it doesn't help. In Preferences=>DataModeler=>Diagram=>Format, I've tried messing with the line widths to see if the change would affect the invisible lines, but no. When engineered to a relational model, the corresponding foreign key's lines do appear. If I create a subview from the entities that have relations between them, the lines don't appear on the subview either. If I change the logical diagram's background color to red, the relations do appear in white (or maybe yellow), though in the narrowest width. (That is, if I change the line width to fat and blank in Preferences, the 90% of the lines that usually appear are there in fat black, but the usually invisible ones are thin and white/yellow.)
How can I get the missing lines to appear? (SQLD 188.8.131.527)
I guess all I needed to do was report it here in order to figure it out!
How I fixed them: Set diagram color to red so that they'd be visible. Right-click the now-visible line to bring up a submenu. Under Format, "Use default" was clicked off. Click it on.
How they managed to become un-default, I don't know, but they're better now. I'll mark this answered but leave this here in case someone else stumbles into the same problem.