If your node is failing to start and/or it's not available in Proposals Discovery and/or reporting as "Connection failed", you could try to restart your node service. There are several ways of doing so:
Using systemctl:
sudo systemctl restart mysterium-node.service
Log in to your NodeUI, navigate to the Settings page, hit a red power of button at the top right corner. The systemctl should put myst daemon right back up when you stop it.
Using Docker you need to restart a container myst:
docker restart myst