Continue to spam click it, then stand on the platform and wait for a second. Not sure if you realize, but if he relogs he might not spawn where he started. Restarting your Minecraft won't work for this, as it isn't his fault, it is the signs fault. They most likely won't reply, and relogging doesn't fix it.
I know...I never said it would be easy. It was just an idea (as I am not sure that this would fix the problem), they don't have to do it.
