How to correct PlantUML Line Path

There are some tricks that you can try, listed below. The layouting itself is performed by GraphViz (dot layouting iirc), and GraphViz simply does this sometimes. Graph layouting is a NP-complete problem, so algorithms usually take harsh shortcuts.

Typical workarounds that I've seen or used include:

• adding hidden lines a -[hidden]- b
• extending the length of a line a --- b (more dashes, longer line)
• specifying preferred direction of lines (a -left- b)
• swapping association ends (a -- b → b -- a)
• changing the order of definitions (the order does matter... sometimes)
• adding empty nodes with background/border colors set to Transparent

So if you really want to have a nice layout, you'll need to put some elbow grease in, but keep in mind that the layout will be still brittle -- if you add/remove items, you might need to redo it again.

Try the options suggested by @Peter Uhnak along with linetype :

skinparam linetype polyline
skinparam linetype ortho

Give better options for lines. Using ortho - (Here)

you will get -