My inventory app keeps showing different stock numbers everywhere and I can't figure out why
When more than one app can write to the same inventory numbers, Shopify will show different stock counts in different places until you find and fix the conflict.
What's going on
You look at a product in Shopify admin and it says 12 in stock. The storefront shows 8. Your POS says something else again, or a connected marketplace listing shows the item as sold out when you know you have units on the shelf. Nothing about your own sales explains the gap, and it doesn't correct itself, it just keeps drifting.
This almost always happens when more than one app or integration has permission to write inventory quantities for the same product. A multi-channel sync tool, a dropshipping or fulfillment app, a POS system, and an ERP connector can each be pushing their own idea of the correct count to Shopify around the same time, and whichever one writes last wins, until the next app writes again a few minutes later. From the outside it looks random and unfixable, but it's really just several systems overwriting each other's work.
Why it happens
Shopify tracks inventory per product variant, per location, as a single number that any app with the right permissions can update. Shopify itself doesn't referee disagreements between apps, it just applies whichever write arrives, in whatever order it arrives. If one update tells Shopify to set stock to 12, and a different app, syncing from a different source, tells it to set stock to 8 thirty seconds later, Shopify has no way to know which one is stale and which is current. It just stores the last value it received.
This gets worse when apps write quantities differently. An app that sends an absolute count is more likely to clobber a concurrent change, since it doesn't account for what happened between its own sync cycles, while an app that sends a relative adjustment is additive and safer to run alongside other tools. Multiple locations compound the problem too: if one app only tracks your main warehouse while another also tracks a secondary or fulfillment-service location, the two can genuinely disagree about what the total figure should be, and both can be correct about their own slice of the data.
5 ways to fix it
Check Shopify's own inventory history first
Before touching any app settings, open the product's Inventory tab in Shopify admin and review the adjustment history for the location in question. Shopify logs each change there, including the quantity delta and, when available, which app made it. This costs nothing and is usually the fastest way to tell whether one specific app is causing the swings, or whether the number is actually correct and it's a display or caching lag in your theme or POS that's confusing you.
Isolate the culprit by disabling integrations one at a time
If several apps touch inventory, such as a multi-channel sync tool, a dropshipping or fulfillment app, POS, and a backup or ERP connector, turn off write access for one at a time, starting with the newest or least-trusted integration, and watch a single SKU for 24 to 48 hours after each change. Keep a simple log of the expected count versus what you see in admin, on the storefront, and in any connected channel so you can pinpoint which integration's writes line up with the drift.
Confirm every app is using locations and stock settings the same way
A common cause of stock looking inconsistent isn't a bug at all. One app may be tracking inventory at a location the others don't check, or a variant may have continued selling enabled after it hit zero. Review your active locations and which ones fulfill online orders, and check each affected variant's inventory settings, since a mismatch here alone can make stock look different in different places even with no sync conflict at all.
Ask each app vendor how they write quantities
Some apps push an absolute quantity, telling Shopify to set stock to a specific number, while others send a relative adjustment, like subtracting two units. Absolute writes are far more likely to clobber a change made seconds earlier by another app or by a sale, since they don't account for what happened between sync cycles. If you plan to keep more than one inventory-writing app installed, ask each vendor which method they use so you can choose a combination less likely to fight over the same numbers.
If the conflict persists, make one system the sole writer
When two or more apps can both push inventory for the same SKUs, the durable fix is usually to pick one system, whether that's your ERP, a primary inventory app, or Shopify itself, as the sole writer, and set every other tool to read-only or to feed into that one system instead of writing to Shopify directly. This is a configuration and process change rather than a code fix, and it's worth doing even if it means a short manual reconciliation while you switch over.
Bottom line
Most inconsistent stock reports trace back to more than one integration having write access to the same inventory numbers, not to Shopify miscounting. Start with Shopify's own adjustment history and your location and variant settings, since those cost nothing and often solve it outright. Only after you've isolated which app is misbehaving does it make sense to change how your integrations are wired together. If you're evaluating new apps, favor ones that clearly document whether they write absolute or relative quantities, since that detail usually determines whether multiple integrations can safely coexist.
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