1. Your own traffic is in the data
Every visit from you, your team and your agency is counted as a user unless internal traffic is excluded. On a low-traffic site this is not a rounding error — it can be a large share of everything.
Fix it in Admin, under the data stream's tag settings, by defining internal traffic against your office IP and then activating the filter. Defining it without activating the filter does nothing, which is the more common mistake.
2. Events recorded but never marked as conversions
GA4 collects events by default. It does not know which of them represent a business outcome. Until you mark an event as a key event, it will not appear as a conversion in reports or be importable into Google Ads.
3. The tag is installed twice
Hardcoded in the template and also deployed through Tag Manager. Every page view fires twice, which halves apparent session duration and collapses bounce rate. The reports look better, which is why nobody investigates.
4. Cross-domain tracking not configured
If your booking system, store or form lives on a different domain, a visitor who crosses over is counted as a new user arriving from a referral — your own site. Conversions get attributed to yourself rather than to the campaign that earned them.
5. Your own domain missing from the referral exclusion list
The same class of problem as above, and it also appears after any payment redirect. If a payment provider shows up as a top traffic source, this is why.
6. Data retention left at the default
GA4 defaults user-level data retention to the shorter option. Change it to the longer setting if you want year-on-year exploration to work, and do it early — the setting is not retroactive, so data already discarded is gone.
7. Consent handled by blocking the script
Blocking the analytics script until consent means visitors who never interact with the banner are absent entirely — and they skew toward first-time visitors, the exact group acquisition work is judged on.
Consent Mode is the better pattern: load the tag with storage denied, then update it when the visitor accepts. You stay compliant and keep modelled data for the rest.
The test that catches most of these
Open your site in an incognito window, submit a test enquiry, then check GA4's realtime report. You should see your session, the page path you took, and exactly one conversion event.
If any of those three is missing or duplicated, something above is the cause.
Common questions
Will fixing these recover my old data?
No. Analytics corrections apply from the moment they are made — historical data stays as it was recorded. Fix it early for that reason alone.
Is Universal Analytics data still available?
No. Universal Analytics stopped processing data and its historical reports have since been removed, so anything not exported beforehand is gone.