Spinning Blade ("Attacking Provides a Stacking Speed Buff Until the End of Combat") was previously 'remembering' the total speed gained across an entire run, removing that value at the end of every combat. So if a character gained 5 speed during a combat they would lose that speed at the end of the fight. Then during the next fight if they gained another 5 speed they would now lose 10 speed at the end of the fight resulting in a net loss that only got worse as the run progressed.
It now behaves as intended, removing only the speed that was gained during the current battle.