Slack install script fails when deployed, works locally, how to debug?

Hi Everyone,

I've been happily using the Slack installation script (found here) for months now but it suddenly stopped working in the past few weeks. When I run the script locally on a Mac, it works fine, but when I push it through Casper (either as part of my deployment workflow or from a Self-Service item), it fails with a "Cannot Install Item" error . The logs in the JSS aren't very helpful, they only read:

[STEP 1 of 4]
Executing Policy Install Slack
[STEP 2 of 4]
[STEP 3 of 4]
[STEP 4 of 4]

Is there another place to look for more detailed logs about how the script ran in the Casper context?

Thanks,

-Mike