Edit: After seeing the comments, I checked my REPL history, and the bad data was still there. luckily with the spaces displayed as \040. Turns out the offending space was \240, which makes more sense. Please disregard this comment.

If you're curious, the problem stems from stuffing JSON in the description field of an external system to do our own tagging. Someone (me) must have copy/pasted from a screwy source. We were pulling out our hair trying to figure out what was wrong with it, and I just stuck it in the REPL, and saw the offending character was a space. Manually deleted the extra space and it was fine. A quick google showed space was part of the convention, and we were like "woah that's weird how did we never stumble across that before." I am embarrassed that I posted this now. My only excuse is that I just got over Covid, so I'm going with that :-).

This was my original comment:

After about a decade of using JSON I just discovered the hard way that you can only have one space after the colon between a key and value. Atleast with the python JSON library.