How can I debug a "Application Error" in my heroku hosted Ruby on Rails web application?

I am getting a "Application Error" screen randomly during the day on my website that last up to 20 minutes.

When I use the basic logging module "heroku logs", it doesn't show any error as if the "Application Error" never occurred.

When I use the new logging module on Heroku, same thing.

GetExceptional doesn't report anything.

How should I proceed to find what causes the error?

How do I check my application error in Heroku?

If you find an error message that you don't understand, try checking out the following resources: Heroku Error Codes (H12, R14, R15, H10, H14 etc.) - https://devcenter.heroku.com/articles/error-codes. Postgres Errors - https://devcenter.heroku.com/articles/postgres-logs-errors.

Where is Heroku error?

Heroku Connect produces logs of its sync activity, which you can access from your log drain. You can also view the logs as they are emitted by clicking the Logs tab. This article documents some of the errors and messages you may see in those logs.