Submitted by DanielArmstrong, also found by pep7siup, mojito_auditor, MrPotatoMagic, nmirchev8, 0xDING99YA, SpicyMeatball, and bart1e
https://github.com/code-423n4/2023-12-revolutionprotocol/blob/main/packages/revolution/src/MaxHeap.sol#L102 
https://github.com/code-423n4/2023-12-revolutionprotocol/blob/main/packages/revolution/src/MaxHeap.sol#L156
MaxHeap.sol#extractMax function only decreases the size variable without initializing the heap state variable.
On the other hand, MaxHeap.sol#maxHeapify function involves the heap variable for the out-of-bound index which will contain dirty non-zero value.
As a result, uncleared dirty value of heap state variable will be used in the process and already extracted tokenId will be extracted again.
MaxHeap.sol#extractMax function is following.
As can be seen, the above funcion decreases size state variable by one, but does not initialize the heap[size] value to zero.
In the meantime,MaxHeap.sol#maxHeapify function is following.
For example, if size=2 and pos=0, right = 2 = size holds true.
So the heap[right]=heap[size] indicates the value of out-of-bound index which may be not initialized in extractMax function ahead.
But in L102 since pos = 0 < (size / 2) = 1 holds true, the function does not return and continue to proceed the below section of function.
Thus, abnormal phenomena occurs due to the value that should not be used.
We can verify the above issue by adding and running the following test code to test/max-heap/Updates.t.sol.
As a result of test code, the return value of the last extractMax call is not (itemId, value) = (5, 10) but (itemId, value) = (3, 20) which is error.
According to READM.md#L313, the above result must not be forbidden.
Modify the MaxHeap.sol#extractMax function as follows:
Since the value of heap[size] is initialized to zero, no errors will occur even though the value of out-of-bound index is used in maxHeapify function.
rocketman-21 (Revolution) confirmed, but disagreed with severity and commented:
0xTheC0der (Judge) decreased severity to Medium and commented:
Note: For full discussion see here
