got the same issue since a long time as well, specially after zoning, once i am in zone it's not bad tho. everytime i zone 2/3 toons are on walk mode ,always.,.annoying , but one in zone /follow keep the run speed until i zone again.
This is a long known bug. To fix, take the character off autofollow before zoning. Seems to only happen when a character zones while still autofollowing.