My initial thought is it is due to the save system and requiring you to "allow third party cookies/storage".
If you right click on the page somewhere and press "Inspect" a developer console should appear. Select "Console" tab.
When the game fails to load is there a red error that appears. That should help narrow issue.
I found this fix for Chrome, and Firefox should have something similar.
Otherwise you can play the game on my domain where this issue shouldn't occur: https://riko-game.netlify.app/