I *swear* there was a post about this but I can't find it, so.. As of todays patch (3/14/23) the 'Well Tended Mount' buff from the Guildhall Stable Hand amenity is breaking the ground speed increase for mounts. If you pick up the 'Well Tended Mount' buff from the stable hand and leave the guildhall, your summoned mount will drop from the regular ground speed buff to a flat 5% ground run speed. This is immediately rectified if you right click and cancel the 'Well Tended Mount' buff. I would suggest temporarily removing the stablehands until the next patch, unless a fix can be pushed while live.
I noticed this too. Took me a while to figure out why all of a sudden my character was practically crawling through the cities. Cancel the buff and back to normal. 'Tis a weird issue.
