I got a CodinGame email: “Someone replied to your comment!”
When I clicked the link from gmail in chrome, it resolved to something like
https://www.codingame.com/training/medium/rubik%AE/solution?id=6901848&comment=23980&expand=true&utm_source=codingame&utm_medium=email&utm_content=comment-answer&utm_campaign=social
Notice the encoded rubik%AE in the URL (which is extended ASCII encoding?). The page never loaded…
I’m pretty sure the correct URL starts with
https://www.codingame.com/training/medium/rubik%C2%AE/solution?
(which seems like UTF-8 encoded %C2%AE)
The notification from the CodinGame notification box seems to work (except the linked solution doesn’t come up, so maybe it was deleted or taken down).