There are several factors that can affect traffic. Check the following points to determine the cause:
Has your marketing department started a new campaign or ended one? Close coordination with marketers ensures that planned changes are known at an early stage. You can test this factor by comparing the current click rates of your strongest campaigns and channels with historical data.
Some traffic changes are due to technical reasons. This can be confirmed by checking if changes are related to a certain device class, browser, or operating system.
Furthermore, the traffic should be examined depending on different characteristics (organization, country/region, etc.). If, for example, a change in traffic only occurs for one characteristic, conclusions can be drawn about possible causes.
If the above suggestions have not led to a solution, changes in traffic may be due to a change in the implementation or account configuration. If tracking is actively adjusted, different measurements of the data may occur (deliberately or unintentionally). Use the developer tools in your browser to check if the tracking request is sent correctly.
Further information on this topic can be found in the training chapter Review of Data Collection.