Combos not working

[Hit by a Parked Car]

I have two in particular that fail to work.
Longsword VIII Fiore Halbschwerten (Up, Left, Right)
Polearm IV Undercut (Stab, Left, Right, Left)

The issue is that I know for a fact that they have worked on this save: I've done them before. The Longsword one just yesterday, in fact. But for some reason, they don't work anymore and I can't get the combo to trigger at all. Has anyone else had a similar problem with other combos? It's not like I'm being perfect blocked or dodged for these to stop working.

[Hit by a Parked Car]

I figured it out. It's pretty weird.

For Longswords, after an overhead, the natural position of the guard after is left. The natural position of the guard after that, is right.
If at any point you made a conscious effort to move your mouse to select the location even though it was a natural position, it canceled the combo.
I tested my theory on the four hitter Undercut combo. For Polearms, a stab's natural position is the same; another stab. But left, right, left, is a natural flow. After the stab, adjust to the left, then leave the mouse alone to complete the combo if you're not interrupted.