Issue
You are running a query on your PostgreSQL database which shows the below error as it exceeds the max_stack_depth value:
Sequel::DatabaseError: PG::StatementTooComplex: ERROR: stack depth limit exceeded
HINT: Increase the configuration parameter "max_stack_depth" (currently 2048kB), after ensuring the platform's stack depth limit is adequate.
CAUSE: PG::StatementTooComplex: ERROR: stack depth limit exceeded
Resolution
The max_stack_depth specifies the maximum safe depth of the server's execution stack. The default value is 2MB.
There is no way you can increase max_stack_depth on Heroku as it is tied with the server config(ulimit). They have to be kept in sync. If max_stack_depth > ulimit, a runaway function could crash the backend process (due to exceeding ulimit) and that would require restarting Postgres.
More information on max_stack_depth for PostgreSQL can be found in their docs: https://www.postgresql.org/docs/current/runtime-config-resource.html