This issue usually occurs when you are running Tabnine on a machine without a GUI. The following options may help:
Use port forwarding to view the config panel from your local machine. If your remote machine's address is firstname.lastname@example.org, and Tabnine is listening on port 5555, the following command will do this: ssh -L 5555:127.0.0.1:5555 email@example.com
You can then access the config panel by copying the URL printed by Tabnine into your local web browser. Note that the string of random characters must be included, or else the config panel will hang with a "Lost connection. Please reopen the Tabnine Hub" message.
Use a web browser that does not require a window manager to access the config panel from the remote machine.
Copy a working config file from another machine. You can find the file location by typing Tabnine::config_dir and adding Tabnine_config.json to the end of the path.