In certain cases you might need to reset your LND tls certificate. This would be necessary if your node's IP adress has changed for example.
connect to the nodl through ssh then type in very carefully :
in the web interface, stop and start lnd again then download the new tls.cert
note: If you wish to connect Zap to the nodl, you will be required to type in the path for the newly donwloaded tls certificate.