PSA: after some debugging via email, we've identified that the issue here.
Because of verbose output in the debug log, the description of the card on Trello was longer than their API limit of 16,384 characters. Multiple file attachments with reports are in the works. With that update, I'll be moving the debug log out of the card description, and into its own attached text file.
Additionally, I'll be limiting the length of the overall description to 16,384 characters, and give a more descriptive error when that limit is exceeded.
Thanks for reporting this issue and taking the time to work it out with me!