Out of stock issue - cannot add to cart for products

Here's a recent issue I ran into. When launching a new store, we had a way for a customer to add high quantities of a product to their cart. This was working during our initial testing and all the configuration on are theme passed QA. Then on the first week of April 2025, the store suddenly had many issues with different products. Here's a few errors we got when adding to cart:

The product '...' is already sold out.

Then on the browser console, the error responses were:

Only 'x number' items were added to your cart due to availability.

The maximum quantity of this item is already in your cart.

The products were not tracking inventory and that was enough to just sell the product without keeping stock. Then I tried setting all the product variants inventory to "Track quantity" and "Continue selling when out of stock", but the issues still happened.

Then I contacted Shopify support and detailed that this is happening on all themes even on the Dawn theme, so this has to be a Shopify store configuration issue. But the response was frustrating; "It's the cache of your store", "Incognito window doesn't show the issue", "Wait until tomorrow until the cache is cleared". Stressful situation with no support, but they did escalate the problem to the Dev Team... but their response was a little infuriating... "Your theme is custom and you need to talk to the theme developer". Did they ignore the whole part that it affects all the themes??? Even the Dawn theme!

So it's time to debug even more. I thought okay if it's just the cache let me create new products for the products that are having issues. I wrote a script that looped through all the stores product variants and added them to the cart with a quantity of 100. Then I ran into a new interesting error:

Only 50 items were added to your cart due to availability. 

It was the same error over and over again. That's a big clue! With a quick Google search "shopify cart limit 50" I finally found my answer. Shopify had recently added a "New Add-to-cart Limit" to stores. And it's set by default! You need to go to Settings -> Checkout -> Advanced preferences (section) -> Add-to-cart limit -> disable option

Anyways, rant over just wanted to speak up about my frustration. I hope you found this blog helpful and don't spend days/hours of your weekend trying to fix this issue and customers complaining that your site is broken because they can't add products to their cart. 

Here's the change log for reference: https://changelog.shopify.com/posts/new-add-to-cart-limit

Shopify should probably put a notice next to the inventory or something to advise of this new change because it conflicts the the "Continue selling when out of stock" logic.