Today I learned!
I will double check with our IT team, they’re the ones that set it up so I’m not exactly sure if it’s on Docker.
Also, a somewhat strange update… I think I solved it, but no idea why or how. 
Here’s my current chain of events:
- The original file was an .xlsx file downloaded from Salesforce, which I saved as a CSV – this didn’t award my test user, but did work with others.
- I tested with just the one email in a fresh CSV – that didn’t work either.
- I tried a few things to clean up the data – this is when I started getting the 502 error and no emails were going through. I think I may have somehow added extra empty fields or something weird here that made the file too large and unable to be parsed, thus the (new) 502 error.
- Pasting the emails from that same CSV into a fresh, new CSV seems to have solved it – my test user was awarded the badge!
… and possibly the strangest part, he’s the only one that was missing the badge?! I don’t know if I fully believe this, because it seems unlikely that this issue would only impact his email and nobody else’s. If it makes a difference, his was the very first email in the file.
Otherwise, maybe he’s just cursed? 