Sibi wrote:They are greyed out completely on every character no matter the level or faction of the character, even the characters I purchased the page and herald on. They aren't counted in my collection at all and I've never had this issue with those pets previous to this recent patch.
Edit:: My friend is missing his guild herald and page as well, he doesn't have the plethora of alts that I (and many other people) have so his hunt to find them is pretty limited (2 characters) and still cannot find them.
The only other reason I can think of that would cause the Guild Herald/Guild Page to disappear or be unsummonable is if you're no longer in a guild. (My horde character left a guild so she can't summon her herald anymore, but it still shows up in the Pet Journal.)
If this is not the case for you, then it's a new bug and as Peanutty
mentioned, submit a ticket or report this in the WoW Bug Forums.
I've been keeping an eye on the forums for any new cases of missing pets, but I haven't come across any missing herald/pages yet. Since these pets aren't really used for anything except purchasing guild items, it's likely players haven't noticed that they're missing.