Same problem with Grass paths, when jumping onto it you "slide" off.
This seems to correlate with MC-156451, same velocity reset, except it is consistent on every sword swing
Your character movement stops/freezes for a split second when you move while hitting a block with a sword is what he's saying.
Just hold in m1 and aim at the ground while holding a sword and sprint/walk and you will notice it.
Bug exists in 1.14.4-Pre4 and 1.14.4-Pre5
Edit: Still exists in 1.14.4-Pre6
Can confirm