A fair number of us are in the same boat. It’s not just problematic for RP, it is gamebreaking. Especially if you have other people who have alt accounts for filler or throwaway NPCS/villains.
Someone else had managed to figure out it is indeed related to not having Dragonflight attached to an account. I was able to replicate this by having my impacted friend try to say something to me at level 70. Not only did I not see what they wrote? I didn’t even see the animation of them talking.
When I was on my leveling 50is character, I could see everything.
There is another thread about this here: /Say and /Emote bugged for people that don't have Dragonflight - #17 by Vanaelia-moon-guard
According to that thread? The developers are aware of that on the EU forums.
However, I do not know how that is progressing, aside from a few update threads in that one. https://eu.forums.blizzard.com/en/wow/t/some-people-cannot-see-s-e-and-y-messages/513924/31
I have not seen any response on the US side of forums, though.
You have my sympathy for how annoying this is. I know what you’re going through. A few stories are effectively halted until things get squared away.