I had the same problem and found how to fix it.
Mozilla Firefow update on my computer and their last version disabled TLS.
You will have this information "Failed to load resources : https://live.plarium.com/vikings/versions/4.7.0/webgl/main.json"
If yes, you can go click on this link, and after that you can click to activate TLS, it will solve your problem.
Thanks it workedI had the same problem and found how to fix it.
Mozilla Firefow update on my computer and their last version disabled TLS.
You will have this information "Failed to load resources : https://live.plarium.com/vikings/versions/4.7.0/webgl/main.json"
If yes, you can go click on this link, and after that you can click to activate TLS, it will solve your problem.