The challenge room is locked but I have full health [duplicate]

This question here:

How do you open the barred doors in the Binding of Isaac?

says I should be able to open these challenge doors with full health. But I've had multiple instances where the room is locked even when I have completely full health. In fact, check this out, I started the level with full health, plus some, and I can't even get anymore! Look:

The challenge room is right there, I have full health, and this is how I started the level. What's the deal?

the-binding-of-isaac-rebirth

Pictures about "The challenge room is locked but I have full health [duplicate]"

The challenge room is locked but I have full health [duplicate] - Crop Asian girlfriends playing video games at home

The challenge room is locked but I have full health [duplicate] - Full body side view of multiethnic girls in casual clothing playing chess at wooden table in bright room decorated with plants in pots

The challenge room is locked but I have full health [duplicate] - Kids Playing with Easter Eggs

How do you unlock Boss Challenge rooms?

Boss Challenge Room Boss Challenge Rooms can only be entered if Isaac has one or fewer hearts of health. Picking up its contents will cause two waves of bosses to spawn.

How do you open the boss room in binding of Isaac?

Boss Challenge Rooms will only generate if Isaac has full health upon entering the floor. They also can only be entered if Isaac has one or less red heart. Its contents are similar to the Normal Challenge Room, but upon picking up its contents, Isaac has to fight two waves of Bosses instead of normal monsters.

How do you open doors in binding of Isaac?

The doors are tied to your health. The door will only be open if you have full health. However, the temporary HP boosts (blue hearts) can serve as a equivalent of the missing red hearts. For example: If you're missing one red heart but have one blue heart the door will open.

How many rooms are in binding of Isaac?

Rooms are the backbone of any floor. At the start of any run, the amount of rooms will be minimal, no more than around 6. But towards the end of the game, they can reach staggering amounts up to around 20. Normal rooms have various objects and enemies in them most of the time.

Darth Maul VS Pre Vizsla

Sources: Stack Exchange - This article follows the attribution requirements of Stack Exchange and is licensed under CC BY-SA 3.0.

Images: RF._.studio, Ketut Subiyanto, Monstera, cottonbro