There could be a number of factors contributing to the increase in the percentage of new visitors on your iOS mobile app since migrating from the Ver4 SDK to Adobe Launch. Here are a few possibilities:
More accurate tracking: Adobe Launch provides more accurate tracking than the Ver4 SDK, which could be resulting in a more accurate count of new visitors to your app.
Changes to app functionality: If you've made changes to the functionality of your app since migrating to Adobe Launch, it's possible that these changes are attracting more new visitors.
Marketing efforts: It's possible that changes in your marketing efforts or campaigns since migrating to Adobe Launch are resulting in more new visitors to your app.
Platform updates: iOS updates could have impacted the measurement of new visitors.
Tracking implementation: You may want to check your implementation of the Adobe Launch SDK to ensure that it's correctly capturing data, especially around identifying returning versus new visitors.
It's important to review your analytics data and see if there are any other trends or changes that may be impacting the increase in the percentage of new visitors on your app. It may also be helpful to conduct further testing and analysis to identify any other contributing factors.