You Sprint Wrong | Cyberpunk 2077 Tips & Tricks
It's a little counterintuitive, but the game DOES reset to the base movement speed once you perform certain actions mid-sprinting. Even if you continue to hold the Sprint key. If you hold it while jumping - the moment you land the character will reset to the running/walking.
To prevent this from happening you can either re-press Sprint (Hold) during the action (during the jump) or use Sprint (Toggle) instead which doesn't have this issue.