slot index and reward index mismatch

[friedger]

Describe the bug
When querying burnchain_rewards and reward_slot_holders the reward_index and slot_index do not match. Example

859045 slot 0 => 31yuSoYmpkV5TDxuMh2GUfchJFef4kHyus

859045 slot 1 => bc1qs0kkdpsrzh3ngqgth7mkavlwlzr7lms2zv3wxe

859045 reward index 0 => bc1qs0kkdpsrzh3ngqgth7mkavlwlzr7lms2zv3wxe

859045 reward index 1 => 31yuSoYmpkV5TDxuMh2GUfchJFef4kHyus

To Reproduce
Steps to reproduce the behavior:

1. run sql query select * from reward_slot_holders rsh where canonical and burn_block_height = 859045
2. run sql query select * from burnchain_rewards br where canonical and burn_block_height = 859045
3. Compare addresses and see that they do not match

Expected behavior
Address in reward_slot_holders and reward recipient in burnchain_rewards should be the same for the same slot index.

[janniks]

@obycode do we know if these should be matching from a blockchain core perspective? I'm not sure if the concepts reward index and slot are equivalent everywhere.

[janniks]

Looked up where they come from on the API end:

stacks-blockchain-api/src/event-stream/core-node-message.ts

Lines 352 to 365 in 3e2d524

	reward_recipients: [
	{
	/** Bitcoin address (b58 encoded). */
	recipient: string;
	/** Amount in BTC satoshis. */
	amt: number;
	}
	];
	/**
	* Array of the Bitcoin addresses that would validly receive PoX commitments during this block.
	* These addresses may not actually receive rewards during this block if the block is faster
	* than miners have an opportunity to commit.
	*/
	reward_slot_holders: string[];

Both are indexes added by the API and show the position in the array given in the event payload.

It seems the mismatch occurs on the node in the functions: calculate_paid_rewards and pick_recipients. I don't think the ordering is important -- just double checking