The bug

When a predicate with the "minecraft:entity_properties" condition with the "is_sprinting" flag is set and is tested on a player while they're mounted, it fails to return true when the player begins sprinting.

Steps to reproduce

Attached is a data pack that stores the success of the predicate on the player into a score; simply install the data pack, and run the /reload command. The scoreboard objective will be displayed on the sidebar.
Summon or find a rideable creature, ride it, then attempt to sprint.

→ The predicate returns false, the score returns 0.