as you have written that everything is setup correct (we trust you in that but you did not share that we can make a check) and you have no error in your server.log (you did not share but you would have mention what you observe in the logs) and your setup over all is correct and has no glitches (you did not share any useful about your setup - what you copied over from what. Means how you build your Frankenstein Graylog … )
So it must be a glitch in the matrix that this happens to you, sorry for that.
No back to business - please remember, this is a community board. All people help here in their spare time. Please invest a meaningful time into your question, including as much details as you could and people will invest time to find the problem in your setup. With the given information - we can only guess.