Indeed, we will be using one object type to represent issues (currently using Weakpoint).
***If I want to show the causal relationships between these Weakponts, what model should I use? ***
I assumed that a Cause and Effect diagram (or Fishbone) would be best however that diagram type does not allow me to use the process weakpoint object. Has anyone tried to show something like this?
Why don't you use the Risk Diagram? The object "weak point" in the EPC is of type risk. In the Risk Diagram you can also involve the "risk category" object to group and categorize the weak points and in this way to model the sources of process problems. So, you will get a kind of Ishikawa diagram.
Speaking of Cause & Effect diagrams, one of the things I've been missing in ARIS is Stock&Flow diagrams, or at least Causal Loop Diagrams.