Data decrease when using Google consent mode

It's not uncommon that users report losing some analytical data after enabling Google Consent Mode.
While this may cause som concern, it's not unusual and the loss of data can be explained by how Google consent mode and Google Analytics' behavioral modeling works.

When you start using consent mode, you may initially see a noticeable drop in your reported data. While this might be alarming, the data integrity will improve over time as Google Analytics' behavioral modeling kicks in.

For behavioral modeling, which compensates for lost data when users don't consent to statistical cookies, to start working, the following requirements must be met:

• Making use of advanced consent mode
  Google Analytics has "built-in consent", which means that you can allow it to load prior consent. It will adjust it's data collection capabilities according to the consent given.
  If you only load Google Analytics when consent has been given, no data modelling can occur.
• A minimal data volume
  To somewhat accurately model data, your website needs to collect at least 1.000 events per day where cookies in the "statistics" category have been rejected for at least 7 consecutive days.
• A minimum user engagement
  You need at least 1.000 daily users creating events who have accepted cookies in the "statistics" category for at least 7 of the last 28 days.

When your website meets the requirements above you should see numbers similar to those you saw before enabling consent mode.
You may still see some gaps when the conditions aren't met though.

To ensure behavior modelling occurs you can try to increase the website's traffic to at the required volumes. More data gives more accurate modelled data though, so the more traffic, the better.