The combat blade’s sprint-attack movement speed buff will now briefly turn off if you press 1 (or whatever key you have assigned to your melee weapon.) This was previously used to prevent auto attacking after holding the heavy attack for too long and allow you greater uptime of the movement speed buff. If you spam 1, you will move slower than basic walk speed, even though you are sprinting.
Other weapons like the Deimos force sword also have this speed buff, I have only tested the Combat Blade (both marks.)
EDIT: After testing further I have discovered that this bug only takes place on the DLC Skitarii class.
This is due to a bug that the Skitarri has with all weapons, which causes weapon switching to cancel sprinting. See this thread:
There are weapons such as the knife and Skitarri Arc Maul which allow you to “equip” them even while equipped, which rapidly cancels Skitarri’s sprint over and over. See this clip, in which the same thing occurs: