Why do the trailers never play?

Server Version#: 1.26.0.5715
Player Version#: 4.80.0 any player I try.

Just wondering - the never play.

You might want to check your router configuration.
Sounds like it has some kind of “DNS Rebind Protection” which can cause remote/online content not to play. Usually such routers allow to specify exceptions (-> plex.direct).

https://support.plex.tv/articles/206225077-how-to-use-secure-server-connections/

Edit: no such issues with trailer playback here.

FWIW I can play Plex TV shows no problem, it’s just trailers.
From the web player on a trailer in chrome I get.
image

Does this happen on all shows + trailers, or do some work? I’ve recently encountered a couple of specific trailers that seem to be broken on the Plex (IVA) end.

Share the specific show/trailer, or share server logs and folks can look.

I don’t recall ever having a trailer work, and sometimes it just spins, and possibly other errors.
If by shows you mean the ad sponsored plex ones, they always work.