Discrepancy in visit metrics across Matomo reports

[heurteph-ei]

Context

From: https://forum.matomo.org/t/discrepancy-in-visit-metrics-across-matomo-reports/53254

Expected Behavior

Each reports should display the same number of (unique) visitors (for the same day)...

Current Behavior

It doesn't:
https://demo.matomo.cloud/index.php?module=CoreHome&action=index&idSite=1&period=day&date=2023-09-19#?idSite=1&period=day&date=2023-09-19&category=Referrers_Referrers&subcategory=Referrers_WidgetGetAll

https://demo.matomo.cloud/index.php?module=CoreHome&action=index&idSite=1&period=day&date=2023-09-19#?idSite=1&period=day&date=2023-09-19&category=General_Visitors&subcategory=UserCountry_SubmenuLocations

https://demo.matomo.cloud/index.php?module=CoreHome&action=index&idSite=1&period=day&date=2023-09-19#?idSite=1&period=day&date=2023-09-19&category=General_Visitors&subcategory=DevicesDetection_Devices

Possible Solution

Unknown

Steps to Reproduce (for Bugs)

See Current behavior.

Your Environment

Matomo Demo Cloud...

[MatomoForumNotifications]

This issue has been mentioned on Matomo forums. There might be relevant details there:

https://forum.matomo.org/t/discrepancy-in-visit-metrics-across-matomo-reports/53254/4

[LenaGadea]

A bit more information on the issue in case it might be of relevance:

• We are using Matomo 4.15.1

• We do not have LOAD INFILE active. We suspect this can be significant to this issue.

• All Active Complements
  [CustomReports] (v4.1.7)
  [DynamicDeviceDetectorCache] (v1.0.4)
  [LogViewer] (v4.1.2)
  [QueuedTracking] (v4.0.7)
  [RollUpReporting] (v4.1.4)
  [TrackingSpamPrevention] (v4.1.7)

[sgiehl]

@LenaGadea Is the site where that happens a site that is tracked or is it a roll up aggregating other sites?

[LenaGadea]

@sgiehl It is a site being tracked. We are tracking a few other sites (with less custom dimensions etc) with no problem. There was as well a roll up aggregating those other websites that started to have great delay on the data as well so we have removed it for now, but the data inconsistency on this site's reports remain.

[Stan-vw]

That's quite a few different numbers across different places.

@sgiehl Are all places using the same query to calculate this metric?

[LenaGadea]

@Stan-vw it is, indeed. Also, the reports were perfectly fine and consistent for months before suddendly going crazy. No changes in any configuration. During that week we created a few custom reports and activated SEO Web Vitals plugIn. We deactivated the plugin right away, and also eliminated all the reports recently.

[sgiehl]

@Stan-vw The queries should be similar in most cases, but group by different dimensions.
This actually should only affect unique visitors, as they are sort of handled special.
I haven't check that in detail yet, but my assumption is, that this is kind of expected.

Assuming the following visits

visit id	visitor id	browser	operating system
1	A	Firefox	Linux
2	B	Firefox	Windows
3	A	Chrome	Linux

So we have one visitor, that came back with different device, but was still recognized as the same visitor.

If you now built unique visitors metrics for those visits you get:

Over all unique visitors: 2

browser	unique visitors
Firefox	2
Chrome	1
Totals	3

operating system	unique visitors
Linux	1
Windows	1
Totals	2

From a dimension point a view those numbers would be correct, as there were two different (unique) visitors using Firefox and one using Chrome.

@LenaGadea Did you maybe start using the user id feature or another method that identifies users across devices?

[LenaGadea]

No changes were made in the tracking method. The correct data was available in the database, it was just the dashboards that that started to track very slowly and showing different metrics.
Since we eliminated the custom reports (there were 5-6, nothing too crazy) the numbers are back to normal, all the reports are consistent and look fine.
Is maybe some sort of performance problem linked to the custom reports?
As suddenly as it started failing it recovered, and the only changes made have been: eliminating the reports and adding a new MySQL read-only node.

[Stan-vw]

That's interesting, thanks for writing this up and great to hear that the problem is not present anymore.
Could you perhaps elaborate what specific reports were in your custom reports, so we can look at those specifically rather than trying the find the issue across all custom report queries?