@kif that’s an interesting issue, I have checked a production app that runs this way and can confirm that I have stack trace, the error is one that is raised manually with raise and not one that happened “on itself”.
We use exception tracking via AppSignal so I must have missed the issue with consistency between real exceptions and what we get in logs.
I also searched for a more “natural” error and have not found one, though I did find ActionClauseError of Phoenix which was reported properly in the monitoring (stack trace included), but in the log I have only seen the “Sent 400 in 6ms”, so that might be your case: Phoenix handles the error in some fixed way which makes it normal case and not an exception which loses the error info for the resulting output.
I would assume you have the same situation, you can test it by adding a manual raise call and see what you get.
In any case I am pretty sure the issue has nothing to do with OS but rather with application environment and configuration.
