Hi There,
Please find my answers below.
==What are possible causes for the stalling?--
This could be temporary glitch, if this gets reproduced on every instance only then something can be done about it,
==What are questions I can ask the user to help isolate the problem?
What Web browser/version are they using, have they tried to switch browser and compare behaviour.
==What are known issues/best practices around file setup to ensure stalling doesn't occur? (my file has 69 slides)
Can you preview your project and observe any problem, are you publish this as SWF or HTML, can you try switching your Published output as well betweeh SWF/HTML5
==Is there any relevance between stalling and the server setup?
You can compare that by enrolling a small set of users 5-6 on the same course after uploading it to http://cloud.scorm.com and verify the behavior.
Thanks,
Anjaneai