Wall of Force cutting through an immovable creature's occupied space

Question

An adventurer cast Wall of Force around a Lich, imprisoning them inside a 5ft hemisphere. The Lich, having Wall of Force prepared too and not fearing death, tries to cast it from inside the hemisphere on themself.

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My group love to cast Wall of Force on my bosses, and it's quite understandable. Preparing my next boss, I realized that I don't know what would happen if someone tried to cast a Wall of Force while inside an enemy's hemispheric Wall of Force.

The spell explicitly states:

If the wall cuts through a creature's space when it appears, the creature is pushed to one side of the wall (your choice which side).

Nothing can physically pass through the wall.

I'm pretty sure the boss won't clip¹ through the Wall of Force but can the spell even be cast and, if so, what would happen? RAW answers are preferred.

¹: a videogame term for an entity abusing the physic and hit-boxes to go through elements usually impassable

Answer 1

RAW does not specify exactly what happens.

It's like you quoted,

Nothing can physically pass through the wall.

Nothing, including another Wall of Force, can pass through. In the PHB page 205 (emphasis mine):

A spell's effect expands in straight lines from the point of origin. ... To block one of these imaginary lines, an obstruction must provide total cover

... And that's where RAW ends on the topic. It does not specify what happens to a creature that is within the spell's effect in your scenario, or even if Wall of Force is considered total cover (this answer alludes to it, but Jeremy Crawford's tweets are not official. This answer is a little bit more convincing, but is still backed up by tweets). If it is considered total cover, than the wall only appears within the original wall. If not, then it extends past. Either way, though, we don't know what happens when something is caught within it, and cannot be pushed.

@NautArch provided this question for more about what may happen.