According to multiple users, the Nexus 6 is experiencing network issues, wherein the phone loses connection to the cell tower and requires a restart to reconnect, although the issue resurfaces after a few minutes. The issue does not seem device specific and has been experienced by multiple users on multiple versions of Android. T-Mobile and Sprint users seem to have been affected the most although people from other carriers and regions have also mentioned having this issue. It's likely this is a software issue and hopefully Google will fix it...
Source: http://www.gsmarena.com/some_nexus_6_users_experiencing_network_connectivity_issues-news-12219.php
