Why is my inventory going into negative despite out of stock settings?

I noticed an issue occurring recently on a store I’m working with. “Continue selling when out of stock” is turned off on all products but we are still going into minus values on certain products.

I feel this may be an issue with Shopify and our product management system. I noticed on a sale recently we initially uploaded 8 products, sold 7 on another platform and stock was showing as 1 on shopify. However, a customer was still able to purchase 8 products on Shopify (while shopify only showed 1 in stock) leaving us with -7.

Has anyone else experienced a similar issue, and did anyone find a solution to stop this from happening?