On Tuesday the new version of the site goes live. The agency confirms everything is delivered: pages display, the cart works. On Thursday you open Meta Ads and see three purchases for €400 spent, where there were around twenty before the release. In the shop, though, orders are arriving more or less as usual.
That's the most common outcome of a release: the store still sells, but measurement is broken. Meta, Google Ads and GA4 no longer receive purchases, and automated bidding optimizes blind. More costly and more discreet, a payment can fail on one browser or one payment method without a single customer writing to you.
The checklist below runs in three steps: before, right after and within 72 hours. It applies to a new theme, a redesign, an app or module update, a cookie banner change or a migration, and every check uses free tools. If your release comes just before a big sales event, add the BFCM 2026 technical checklist, which covers Black Friday in detail.
What breaks most often
Causes are ranked from most to least common. No study puts numbers on them, so the order is indicative.
| Cause | What you see |
|---|---|
| Tracking code pasted by hand into the old theme and not carried over to the new one | No events at all, site-wide |
Funnel event renamed or emptied (add_to_cart, begin_checkout, purchase) | Purchases arrive at €0 or with no currency |
| Google Tag Manager container missing, duplicated or with a different ID | Nothing comes through, or every purchase is counted twice |
| App or module updated: extension switched off, authorization to renew | A single channel (Meta, TikTok, email) stops reporting |
| New cookie banner that blocks tags | Sudden, steady drop in every conversion |
| Missing redirects or lost URL parameters | 404 pages on your ads, campaigns losing their source |
| Performance degraded by new scripts or heavy images | Mobile conversion rate falling with no other explanation |
| Payment or funnel failing on one browser or payment method | Orders falling, no error message |
The last row is the rarest and the most expensive. The first two are the most frequent after a theme change: Shopify states that code edits made by hand or by an app are only carried into the new version if they don't conflict, otherwise you have to copy them over yourself.
Before the release
- Record a 7-day baseline: orders, revenue, conversions seen by GA4, Meta and Google Ads, mobile and desktop conversion rate. Without it you can't tell afterwards whether a 12% drop is normal.
- List everything that measures: GTM container, pixels, apps, scripts hard-coded in the theme. Keep a copy of the custom code, as Shopify recommends before any theme update.
- Work on a copy. On Shopify, the new version stays a draft until you publish it. In Google Tag Manager, test the draft in Preview mode before publishing.
- If URLs change, list every old address with its new destination. Google recommends permanent redirects from the old URL to the new one, without sending everything to the homepage or chaining redirects.
- Plan the rollback. On Shopify, the previous theme moves to the draft themes section when you publish the new one. In GTM, every publication creates a version, and an earlier version can be set as the latest version and republished from the Versions screen.
- Pick the slot: no campaign launch, no start of sales, no Friday evening. Tell the acquisition team, because if they change budgets at the same time you won't know what caused what.
Right after the release: the first two hours
Run the full journey in this order.
- End-to-end order. On Shopify, the test payment gateway simulates a transaction with no charge. While test mode is on, customers can't place orders: do it at a quiet hour, or place a real order and refund it.
- Google Tag Manager. In the workspace, click Preview, enter the site address, then Connect. Walk through the product page, add to cart and confirmation: the debug interface lists which tags fired, in what order and with what data.
- Meta. The Meta Pixel Helper extension, now renamed Meta Ads Data Advisor, shows whether the pixel is present and sending events. Open the purchase event and check
valueandcurrency. - GA4. In Admin, under Data display, open DebugView. Your purchase should show up with its transaction ID, amount and currency. Events don't appear there if the visitor hasn't consented to Analytics cookies.
- Browser console. Open developer tools (F12), go to the Console tab and repeat the journey. Red lines are JavaScript errors: a single one at the payment step is enough to block a purchase. See also the JavaScript errors that cost sales.
- Cookie banner. Run the journey twice, accepting and then refusing. Tags should fire in the first case and stay silent in the second. The article on the cookie banner and lost data covers the cases.
- Redirects. Click your ten most-used old landing pages from ads. None should lead to a 404, and
utm_parameters should survive the redirect. - Mobile and a second browser. Repeat the purchase on a phone, then on Safari if you tested in Chrome, with every payment method on offer.
If something doesn't come through, the article on the Meta pixel no longer reporting purchases walks through the diagnosis tool by tool.
Within 72 hours
Some defects escape testing: they depend on a browser, a time of day or a payment method. Every morning for three days, compare with the baseline you recorded before the release.
- Shop orders against purchases seen by GA4, Meta and Google Ads. The ratio should stay close to what it was before the release. A falling ratio signals lost measurement, a ratio above 1 signals duplicates.
- Average value of reported purchases: a €0 amount or a missing currency shows up in the average.
- Conversion rate by device: a drop on mobile only points to performance or a script.
- 404 pages hit from your ads and emails.
On day three, decide: keep the version, fix it, or roll back.
Who does what
| Who | What they do |
|---|---|
| Agency or developer | Delivers on a copy, carries over the tracking code, prepares redirects and the rollback, fixes JavaScript errors |
| Marketing and acquisition | Records the baseline, tests GTM, Meta and GA4, compares conversions for 72 hours |
| E-commerce manager | Places the end-to-end order, checks payments and promotions, signs the final validation |
One rule avoids this trap: delivery is accepted only once marketing has validated measurement. Without it, the agency considers its job done and marketing finds the problem three days later.
What a failed release costs
The figures below are examples, to redo with your own.
- Lost sales = revenue per hour × number of hours × share of orders affected.
- Ad budget without signal = daily budget × number of days without reliable measurement.
For a site doing €30,000 of revenue a day, or €1,250 an hour on average, a payment method that carries 25% of orders and goes down for 8 hours costs 1,250 × 8 × 0.25 = €2,500.
For a budget of €1,500 a day, a pixel that stays silent for 3 days means €4,500 spent without reliable measurement. That sum isn't lost in full, since the clicks did bring visitors. But automated bidding learned without seeing purchases. According to Google, the Smart Bidding learning status never lasts more than 7 days, and performance can take one to two conversion cycles to settle. The full calculation is in what a dead pixel costs.
Keeping it from happening again
The checklist protects release day. It doesn't cover the following Tuesday, when an app updates itself or a colleague edits a script. A tracking audit every quarter catches what has drifted between two releases.
Between releases, Korvus takes over. Its snippet watches the site continuously and alerts you, with the impact in euros, when a conversion pixel stops firing (dead pixel alert) or when performance drops on paid traffic (performance drop alert). The Shopify integration installs in 10 minutes. If you install it before the release, you get a reference period: the 28-day learning period starts at installation. To see where your measurement stands today, run the audit; the sentinels show what an alert looks like.
Frequently asked questions
What should I check after updating an e-commerce site?
Place an order end to end and confirm the purchase reaches GA4, Meta and Google Ads with the right amount. Also test the cookie banner, redirects and mobile, then compare your orders with your ad platforms every morning.
Why is my tracking broken after a Shopify theme update?
Most often, tracking code pasted by hand into the old theme wasn't carried over to the new one. Shopify says code edits are only included when they don't conflict with the update, and recommends saving a copy first. A funnel event renamed by the new theme has the same effect.
How long should I monitor the site after a release?
Check closely for the first two hours, then every day for 72 hours. Extend it to a full week if your sales are uneven: some defects only show up on high-traffic days.
Who is responsible for tracking after a redesign?
Settle it before delivery. The agency or developer delivers a working site, and marketing confirms that measurement is intact. Until that sign-off, the release isn't finished.