yesod 1.4
LANG environment variable issue?
Temporarily disable all but Yesod
Try single-threaded build
Update to yesod-1.4

Pinging @gregwebs. Could you have a look at this commit, and in
particular mkMongoKey? I can't figure out how to get this to work under
persistent 2 (I frankly don't understand how it worked under persistent
1 either).