We are currently investigating an issue affecting Snowflake connections in dbt Cloud Development environments. Users attempting to set up new Snowflake connections with account identifiers containing underscores experience authorization failures.
Existing sessions are not impacted, this only impacts new users re-authenticating to snowflake in the developer credentials.
Workaround: Replace underscores with hyphens in the Snowflake Account field in your dbt Cloud connection settings (for example, my_account → my-account) and avoid using dynamic configuration containing {{env_var()}} config in the hostname field.

Please reach out to support@getdbt.com if you have any further queries.