The customers use licensing feature to enhance platform services. Subscription licenses can be renewed and even ported to similar Juniper hardware device. Removing/adding license on a device leads to the question, does this process of removing and adding license affects data traffic?

The process of adding a license is designed to be non-intrusive and should not disrupt ongoing traffic. However, if the license enables new features (such as IPS or content security), those features might start affecting traffic based on their configuration and policies.
 

Addition of the features like MVPN-instance-capacity, EVPN-MPLS and other similar services itself should not directly impact traffic but there are some specific scenarios and configurations that could potentially cause issues.
 

Adding a BGP license to a device mainly enables routing features and doesn't directly affect data traffic, but configuration changes can indirectly cause issues like NAT route flapping, traffic loss from incorrect shaping rates, or drops from rapid EIM mapping changes.

None of these services should directly disrupt ongoing data plane traffic; however, existing issues on the MX Series platform might impact traffic under certain conditions. Therefore, it's recommended to review these known issues and ensure your device is running a stable and updated version of Junos OS to minimize any potential risks.

Best practice to avoid any potential issue or loss in traffic is to add licenses during MW. 

For more information on license usage, please refer to the documenation: Juniper Software License Model Overview