Of all the answers, including the currently accepted one, only J. A. Streich has accepted V2Blast's suggestion to update to accommodate the then-new (2020) Sage Advice ruling, which said:
What happens to objects brought inside and left inside Mordenkainen’s magnificent mansion when the spell ends? The intent is that the objects are ejected from the mansion when the spell ends and appear in unoccupied spaces closest to where the door was. This intent will be reflected in future printings of the Player’s Handbook."
Since then we have actually been able to see the new version of the spell, currently available on D&D Beyond, which says (emphasis mine):
When the spell ends, any creatures or objects left inside the extradimensional space are expelled into the open spaces nearest to the entrance.
However, even before this change, it was possible to refute one of the OP's assertions, "The spell description does not specify if you always conjure the same Mansion, or if it is a different one."
While it is true that the spell description does not explicitly address whether a new-cast mansion is the same as one previously cast, the spell does say:
It contains sufficient food to serve a nine-course banquet for up to 100 people.
The PC's may eat this food, reducing the total amount, during the 24 hour duration of the spell. If this was the same mansion on the next cast, it would not then have food for 100 people; it would have lost the food eaten since the last time it was cast. Thus the spell, when cast, would not match the description given. Further, every time the spell was used, it would be of decreased utility, until the caster was summoning a mansion with no food inside, which is both a mechanic unlike any other spell and a strange limitation for a spell of 7th level.
The spell also says:
The place is furnished and decorated as you choose...Furnishings and other objects created by this spell dissipate into smoke if removed from the mansion.
It does not say that furniture removed from the mansion returns to it; rather, such things disappear. If they are no longer present when the spell is cast again, then it does not match the spell description which says the caster may furnish it as they choose. And if the chosen furnishings are present even after 'disappearing', then it is clearly not the same mansion.
Thus from the spell description itself it is strongly implied that you get a new mansion upon each casting, and can thus re-arrange the layout each time. This is in direct contrast to the spell demiplane which explicitly gives the caster the choice to open a portal to a new demiplane or one previously created, and which also explicitly says that any demiplane created persists indefinitely after the casting, even though the door lasts only one hour.