Shopify orders fulfillment webhook triggering at strange times

[mv5]

I have a script to update inventory (self hosted) on orders/fulfill webhook POST request. 

For some reason, this webhook is triggering well after my warehouse team is gone and all orders have been shipped for the day. 

Any idea on why I'm getting fulfillment notifications for orders that shipped out yesterday at 7pm after we are closed and nothing is being shipped?