Whenever a user comes to your site through a direct source, but had come to your site previously from another non-direct source (organic, CPC, or referral) then the first session that happened within the time window specified by Campaign Timeout will overwrite the medium and source of the direct visit (or visits).
To prevent that, we recommend changing Timeout period from 6 months to 4 hours. But, changing Campaign Timeout has a major impact on traffic sources and thus shifts interpretation of GA reporting as a whole. You can read more details about this issue in this article.
Therefore, we recommend making a new property in GA that will run parallel to your current one.
Unfortunately, Google does not allow a property to simply be copied.
So, you have to set-up a new property with all its settings as close as possible to the old one. Don't forget filtering out payment gates and setting logins from Google and Facebook as referral traffic. The most crucial settings to check that you are measuring the same way include: 1) Conversions, 2) Revenue and 3) Goals.
Find Timeout option in Google Analytics settings.
Go to Admin > Property > Tracking Info > Session Settings
2. Change the Maximum Campaign timeout value and hit apply. We recommend a period of 4 hours.