If you run into this issue, please contact Olive Tree Software support at support@olivetree.software.
Internal Techs Notes
This issue was due to Candle adding a stylesheet record in the database, but not actually having any bytes in the styles column. Here's the commit that fixed the issue: https://github.com/OliveTreeSoftwareLLC/candle-server/commit/d19ec800814fb5f6de0f845cf07f68892bbaa8c2
To resolve the issue:
1. Run this command in Setup > Query Tool:
DELETE FROM stylesheets;
2. Update the software to the latest version. (or restart it if it's already the latest) This will trigger a report re-import.
Reporting should work again.