It is actually working consistently, but it's really finnicky, three things I noticed.
- If you jump towards a ladder, you have to repress up at the right time, if you keep it pressed during the jump it will not respond.
- The area where the ladder responds to up is quite narrow, in other words, the timing is quite specific.
- When you jump up a ladder through the top of a screen, you also have to repress quickly after the scrolling, otherwise you will fall down
So, I do fully agree with you, the climbing could be better. But that's really my only gripe in this game.