Hey everyone,
I’m hoping for some guidance on a cart behaviour issue we’re struggling to diagnose.
On some customer sessions (not all), when a customer adds one unit of a physical product (inventory tracked) to cart, the quantity automatically updates at checkout to either:
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100 units, or
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The total available inventory for that SKU (sometimes above 100, sometimes below)
When this occurs, the customer:
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Cannot change the quantity back to their intended amount
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Even if they manually adjust it, the cart reverts to the inflated number
What makes this difficult to isolate:
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We cannot replicate the issue internally (office testing, multiple devices/browsers)
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It does not affect all customers or all carts
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Some affected customers used Shop Pay, others did not
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One confirmed they were using Firefox, but others were on different browsers
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No consistent product, customer, device, or checkout method pattern has emerged
Relevant setup details:
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Products are physical goods with inventory tracking enabled
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Inventory quantities are imported via Exo (ERP → Shopify)
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No manual quantity rules or minimums are set at product level
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Behaviour appears to trigger during checkout, not at add-to-cart stage
Troubleshooting already completed:
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Reviewed cart, product, and checkout-related theme code
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Attempted overriding default quantity behaviour
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Removed and refactored conditional logic (
if / thenstatements) to force customer-entered quantity to take precedence -
Issue persists despite these changes
At this point, we’re unsure whether this is:
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A theme-level cart script or AJAX issue
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An inventory sync edge case from Exo
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A checkout / Shop Pay interaction
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Or a browser/session-specific bug
If anyone has experienced something similar, or has suggestions on:
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Logs or reports we should inspect
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Known conflicts with inventory imports
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Cart scripts or checkout extensions that can override quantities
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Ways to trace or capture affected customer sessions
…I’d really appreciate your insight!
Thanks in advance,
Chel