Full answer:
- EnumerableSets takes 2 slots on the StorageLayout as opposed to DynamicArrays taking only 1 slot as the base slot where it is stored the array's length.
- Immutable Variables don't affect the storage layout. Immutable variables as well as constants are stored on the contract's bytecode.
After the upgrade, the owner will no longer read from slot 2, instead, will read from slot 3, which is empty since owner's value is stored on slot 2. So, owner will be address(0).
This is a preview of the actual storageLayout for the 2 contracts: