So, when I use /zh here, or /zh tp, the horse I'm prompting disappears. I can't get it to reappear.
It is saved in the database, and I can hear it near me, but it is invisible.
I've tried switching the TP method to 'old' but that doesn't change anything.
Running SpigotMC, 1.12.2

Are you sure that it occurs with /zh tp too ? This command only teleports the player.

I found that some combination of WorldGuard and Essentials/GroupManager was conflicting.
I've managed to make it work, finally!
Thank you SO much.

Is there a way to edit a horse's statistics? Make it faster, slower, etc?

Nice ! Could you describe the steps (config lines) taken to fix that ?

It's not possible as of now (only with /zh spawn) but I was thinking of a /zh edit command