I have experienced this before. At the end of the day, debugging a few things helped:
- Check that the remote machine has a connection. In some cases, the servers I hosted my remote on crashed for whatever reason. I just called the service provider and notified them that I couldn't connect to my machine. Moreover, in other institutions I worked in, my user had to be logged into the remote machine to be accessible. In any case, check that all the requirements for remote connections on the host are fulfilled.
- Check that your remote machine accepts your connection. I'm not sure what you've set-up on the remote to protect your connection to it. I have, for example, established connections allowed from a VPN. So only me and anyone else I know that has access to the VPN can connect to the remote. If you set this up, your error could be that you forgot to activate the VPN. If I had a nickel for every time that I did that...
- Check that you have a stable connection as well. At the end of the day, this is basically checking (1) for your local machine.