Game completely died at the first boss.
at the end of the level beforehand it said "game over" at the end of it.
after restarting I was in the boss room, the boss was rapidly altering between two poses.
"OK" I thought to myself "let's ignore this, kill the glitched boss and see how the rest of the game plays" only to find my arrows stuck in the air in front of me and doing no damage.
Disappointed I walked to the edge of the level, where I found the portcullis was glitched too and I could pass through it. only to experience a game-over screen. Hoping that the game may sort itself out I pressed restart, only for it to put me back at the start of the level with nothing changed.