Orders Merging Issue – New Order Products Adding to Old Completed Orders

I’m facing a critical issue with order creation in my Magento2.4.6 store. Sometimes, when customers place new orders using credit limit payment method, instead of creating a new order, the products are getting merged into their old completed orders.

For example:

  • Customer has an old order containing products A, B, C (already
    invoiced and shipped)
  • Customer places a new order for products D, E, F
  • Instead of creating a new order, products D, E, F get added to the
    old completed order
  • The old order’s order_id remains the same, but the increment_id gets
    updated

Key Points:

  • This happens rarely
  • Regular payment methods work fine
  • The old order might be months old and already completed
  • We see the old order_id in logs instead of a new one
  • This creates issues with order management, invoicing, and shipping

Any guidance or similar experiences would be greatly appreciated. Happy to provide more details if needed.

Thank you in advance for your help!