When attaching connectors to different magnets (other than "centre") re-opening a DMN diagram resets connections to the "centre" magnet. IDK if this is an issue with writing magnet positions to the XML or recreating the connections from the XML.
In DMN Designer, change magnet position in:
- Source node
- BKM, BKS , Decision, Input
- Target node
- BKM, BKS, Decision , Annotation