Want some info on how the mount auto sprint actually works, cant find this info anywhere. Having recently reached Art 1 in Training i ticked the small auto sprint box and my horse auto came to a juddering halt and threw me off.  Does this mean auto sprint cannot be used while auto pathing or in partcular, afk auto pathing? Auto sprint only works when manually holding down auto run constantly?

You need to make sure that if the horse learns sprint that the skill is leveled to 100%, otherwise you try to auto sprint and the minigame will kick in. If youre afk leveling horses its best not to have it ticked because as soon as they learn sprint they will throw you off ^^

Wow, thank you Aastrid! Yes indeed my Sprint skill is far from being 100% so thanks to your easily explained  answer i now know the reason. Such a simple thing to overlook but  so important, i appreciate you replying and clearing up my issue.

Also be aware a lot of the autopathing isn't optomized for auto-sprint. Many routes between major cities will get you stuck, so make sure you don't afk, similar to auto-breezy sail and boats (though not quite as bad).

Auto sprint is pretty shitty you get stuck on buildings, trees, fences, even run into mob zones (and get stuck there), off cliffs or end up in the water... ¯\_(ツ)_/¯

You say it sucks, but despite the small & not often hiccups it's FAR better than just the regular speed your horse moves at. They've also added new options for auto pathing exact or smooth which you can find under General Settings, Misc. Exact seems to work better than smooth imo