Where does the BUCK STOP when troublehsooting multisite installations?

I'm troubleshooting an issue with Views & Draggableviews modules for the past month--its driving me bonkers. Two of my installations on my multisite are not working and one is, except when it isn't--intermittently.

The big question is understanding where are these Views troubles are on the continuum from:

• admin settings (conflicting modules, deps, individual site settings, mysql table issues),
• module issues (buggy modules),
• core/multisite issues.

To put it in other terms, is there a rule of thumb when one site of a multi-site is working and another is not? If the sites are not displaying Drupal core errors, URLs are resolving to the correct sites, existing content is accessible, etc. Can I eliminate multi-site as a cause for other module and core issues?

Programmatically is there really any difference in processing a request?