This could be about the other issues with Second Life, but also I just updated the viewer to 18.104.22.1683053.
The display name is not showing for most avatars in world, just the user name. This applies to me too. If I hover my pointer on an avatar, I get just the user name. If I use the nearby list, then it is just the user name showing too.
One strange thing is that out of 8 avatars I checked, 1 was showing display name correctly.
When I check my SL profile, both names are showing and if I go to edit profile, then it is all correct.
I did check preferences settings and seems nothing changed because of using the updated viewer.
Thanks for any help.
Update - the problem just cleared. It seemed to clear when I received an IM from someone.