Try reviewing your Adobe Launch implementation for any tracking issues that could be causing this. Maybe the first party cookies aren’t getting set correctly or there could be issues with cross-domain tracking. Check for any incorrectly implemented filters in GA360 that could be excluding return visits. Also, consider any recent changes made to your website that may have impacted tracking. For instance, if you recently updated your site to force HTTPS, users who previously visited the HTTP version of your site will be considered new again on the HTTPS version. Look into browser related impacts as well – cookie policies of browsers can vary and this might affect tracking. Lastly, ascertain whether this issue is occurring across all browsers or is it localized to a specific few.