@teamasphalt from having a quick google it seems more likely this is due to NetworkManager
attempting to take control over the interface.
A quick way to test this would be to connect to the device over serial and stop the NetworkManager
service with systemctl stop NetworkManager.service
and then try out tshark
again. If this works you could have a go at following this guide to enable you to have both NetworkManager
and tshark
running side by side.