Nightingale Legacy Portal
This fight is incredibly glitchy if one does not stay at the top of the tower the entire time.
The Knight and the Rooks have decent pathing down the stairs until you start jumping off ledges, then they will start racing up and down the staircases and occasionally fall off (you can also cause this to happen by pushing them off ledges yourself).
If they land on a lower level they will race back up, but one of the lowest levels of stairs actually has a jump that they can't cross and will cause them to teleport back up or get stuck there without moving (pushing them off the edge repeatedly results in them teleporting back to the spot they were stuck at, still glitched out).
The Knight also gets stuck in some of the tight corners and only comes unstuck if you make him do the charge attack.
The Knight can be made to fall off ledges for damage (yay) but will teleport back to the top of the tower with full health and be glitched out if he falls past that one spot on the stairs with the jump (sry, I thought I had a screenshot but I forgot. It's the very first staircase after the entrance).
In one instance boss fell off the tower but did not teleport back up (the rooks did though) and I was able to complete the fight normally on the ground around the tower.
Note that I am playing on Extreme, so the Rooks and Knight are scaled at level 120 (maybe the fall damage would kill them otherwise? The Knight takes about 1/4th damage if he falls all the way down, same for the Rooks).
Something similar just happened to me, but I died and respawned. I went back to the tower immediately, but now the Knight and Rooks do not fight at all, they just stay in one place, not including if you push them. They do take damage and will eventually explode, but they drop no items at all.