I have analytics on the current site, until recently, without implementing user_id, I analyzed traffic and saw certain data on: direct, cpa, etc., the other day I decided to implement user_id and place the solution on the site, and now in traffic report, direct indicators began to grow and cpa began to fall.

User ID is implemented as follows: a variable is created that is placed in cookies, a configuration tag is created in GTM where this value is set in Configuration settings. user_id is sent in every event and exists at the very first analytics event, that is, there is no option where the user_id would be missing when any event occurs.

Please tell me why the data in the report began to differ so much, what is the reason for this and how can this be corrected? Or is it a matter of analytics itself?