If you are using custom security roles for the user and also using the CRM Mobile applications, you might run into a permissions issues due to some new entities. One of the new features of CRM 2016 is Custom controls for the mobile application. To support this, there are three new entities that are added. The out of the box security roles like Sales Person are modified during the upgrade to have read permissions to these entities. If you are using custom roles, though, those custom roles do not get updated automatically, and you will need to upgrade them separate from your upgrade to CRM 2016.
To be able to run the CRM Mobile application against a CRM 2016 organization you need to make sure the user has read to the following three highlighted entities.