I noticed this too. Sometimes, mobs and NPCs only spawn at about 20 yards away (about mid range of a Mage Frostbolt (35 yards) for ex) o_O
Though, if you go backpedaling for a dozen yards, they will stay visible until about ~ 40 yards then despawn.
But they won't reappear till ~ 20 yards lol.
Battlegrounds must be a huge pain in the ass with this o_O
That view distance / spawn / visibility is not a bug, it's set server side to prevent further lags and is well known on heavy populated private servers...
I remember a french wotlk server where there was no raid lockouts which got hugely popular (and primarily populated by immature kids) named Millenium Servers where they had to decrease view distance up to the point where YOU COULD NOT SEE ANYTHING PAST 20 YARDS ALL THE TIME.
It was pretty awful, considering you should normally be able to view, for ex, Stables and opposite faction players from the other side of the map lol.
With that awful view distance you couldn't even view them from the other side of Blacksmith when you were arriving ahah.
In the end that server became shit cause the dev were only looking at 'donation' profits and didn't fix the many bugs plaguing it. Now the population is at about ~ 1000 players max during peak evening / weekend hours yet still with crappy view distance lmao.
Tl ; dr please find a way to reduce lags when too many players are logged in BUT without reducing view distance!
Quite sad to be almost in melee range to be able to cast a 35 yards spell, isn't it?

This is a signature until I can bypass that damned 502 ERROR when I put an IMG tag in my sig and try to submit it.