If you have aggro from multiple snared/rooted mobs throughout the area/dungeon? Then those mobs automatically go on your hate list. Logging out and back in will clear your/pet hate list.
If you’ve got aggro you can temporarily wipe your pets hate list with /pet wait, but if you’ve still got mob aggro? Then the pet hate list will again tally all those mobs still on your hate list back onto its hate list…
I don’t think I’ve ever read or seen a developer confirm the exact nature of /pet behind. Does /pet behind command reset the hate list and then simply /pet follow in one simple command line versus two command lines of /wait /follow? Well, anyhow, I’ve always used /wait and /follow just to be certain.
I do seem to recall that /pet behind was added long before we had nano crystal pet warp - pets simply got very lost because the game AI or code or whatever needed some serious work and /pet behind seemed like it was added as a workaround for bad coding. I could be wrong about that - it was all so long ago.