The unexpected behavior is seen on 2.9.0.beta8 (d716e32a32). I remember that the global notice was functioning several days ago on 2.9.0.beta7.
I thought that it may have to do with the search banner component, but disabling it changed nothing.
hi!
I could not reproduce on a new site on the exact commit you mentioned; the global notice shows up correctly after being set:
Could you share more details about when/where it’s not showing for you?
Does it show in safe mode?
Hi!
The global notice didn’t show up anywhere.
Oh right I forgot the safe mode before. I just entered safe-mode under various condition set, the global notice shows up. I managed to figure out that it’s the custom wizard plugin interfering. Disabling the wizard plugin brings my global notice back.
Thank you for shedding light on the issue. Though I can’t imagine how can this plugin have to interfere with the global notice… 
@angus Could you take a look at this sometime?
Yes, the custom wizard plugin removes the global notice, but only on wizard routes. Could you just link me to your site so I can see if I can reproduce the issue.
(these posts can be moved to the custom wizard plugin topic)
Ok, I will pm you the link.
Ah I see the issue. Now fixed. Please update the plugin to the latest commit.
Sorry for the inconvenience!