The 7 tombs in act 2

[Ruvanal]

Also, unrelated, for act 3, the game do some rnd[2] and thus pick among 2 things. Is there something similar there? No other such randomness things are done at the same part of act initiation.

How many times? There is the matter of the positioning of the 6 temples in the 3 of the areas of Kurast which have 2 temples each.

There is also the posibility it is determining how to layout the connectivity of the jungle area. Sometimes the Spider Forest will connect directly to the Flayer Jungle and the Great Marsh, while other time the connection is only to the Great Marsh. Off hand I suspect it is for setting up which pattern for this to use.