Shutdown wall message not displaying

You won't see the wall message on your current logged in user on the physical system. However, anyone that is logged in via ssh will see the wall messages. Also, being logged in from SSH yourself you would not see the shutdown message as you would have to send it via sudo which will disrupt your ability to see the wall message but others logged in via ssh would still see it on the same system.

Also, the wall messages from shutdown have a 15 minute time limit on them. Anything over 15 minutes will not show up on the wall. It could be a bug but I am not 100% sure as it could be by design. Anyway, I did test with 16 minutes and at 15 minutes left, no message.

Here is an example in screenshots. The one on the left was ssh localhost and the one on the right is just a normal terminal that is opened. If you notice the one on the right is not receiving any of the messages.

Hope this helps!