Assisted-service has a size limit on the additionalTrustBundle that can be supplied to it. If this size is exceeded, the only clue will be the most cryptic of possible messages in the agent-register-infraenv.service log:

Failed to register infraenv with assisted-service: response status code does not match any response statuses defined for this endpoint in the swagger spec (status 422): {}

We should validate the size in the installer before generating the agent ISO so that we never have to debug this issue.