Identify & Fix sudden drops/increases of metrics in Google Analytics

Recently I notice a sudden drop in bounce rate with one of the analytics accounts I have been working on. Although, initially I was very happy since it had been implemented a new map feature..I soon applied my rule of "when is too good to be true... it's too good to be true" when I realised it was a 40/50% drop. Since

Graph showing a sudden drop in bounce rate in google analytics

Key: Light blue (Bounce rate) / Blue (Sessions) - Last week shows the change after removing duplicate tags

After quickly looking at Google Tag Manager's setup I found analytics tags with the same ID, although one was universal analytics tracking code and the other classic. In addition the new Google Tag Manager container that was correct (only had one tracking code) had not been published.

I also noticed this was a common problem after doing a quick google search, and so I decided to write a quick blog post on how to identify it and fix it.

Identifing duplicade tracking issues in GA

  1. Sudden drop/increase in Session metrics such as Bounce Rate, Page views, Av. session duration.
  2. All these sudden changes happened cross channel, device, time and geographical region.


  1. Check Google Tag Manager or source code of website for tag duplication with the same identifier.
  2. Check webpage source code for duplicate tracking codes.
  3. Check if any of your other tags also implement your analytics tag (sometimes paralel services allow you to add a Google Analytics identifier for tracking and they will be embedding the GA tag as well).
  4. Confirm if the live container has the latest fix.

Note: As precautionary measure you can initially setup a secondary tracking method (such as mixpanel or KISSmetrics) to evaluate GA data quality. Any discrepacy above 10% in GA should be considered a setup issue.

You might also want to read:

  1. Google Analytics common setup issues
  2. Google Analytics - How to setup your tracking code