Sometimes the nodes inside the Decision Service are positioned outside from the Decision Service when the .DMN is saved an open again.
I was unable to map exact when this happen, but I noticed that this happens depending on the changes you do in the position and size of the Decision Service and its inner nodes.

I recorded a video with 2 minutes when the issue happens in the last seconds.

As it can be notice it takes lots of trials to reproduce the issue.

Also I was unable to reproduce the issue in the Business Central, so I'm not sure if it is related to DMN Editor in VS Code or DMN Editor itself.