A self-referral in Google Analytics is traffic that comes within your own domain.
Self-referrals can cause inaccurate session count and are usually caused by configuration problems such as missing tracking code and improperly configured cross-domain tagging.
Self-referrals can have a significant impact on your data performance. It can affect acquisition, behavior, and conversion data. Therefore, you’ll need to fix it right away because inaccurate data can lead to bad decisions.
How to fix self-referral?
Google’s Tag Assistant Recordings can help detect self-referrals. It can notify if there are any cross-domain tracking cases and whether your pages are correctly tagged or not.
Other Google’s helpful tools are Google’s Tag Manager and Universal Analytics.