Google App Engine doesn't seem to like rogue thread usage. Compojure-api usesFGE for optional Swagger Spec validation, which uses rogue threads. SeeIssue #227 for details.

To run compojure-api apps under GAE, you should use the following require-statement (requires version1.0.3 or higher)

[metosin/compojure-api"VERSION":exclusions [[metosin/scjsv]]]