Query with PROCESS of multiple input optimisation failure

[GrigoriyPA]

Reproduced on query:

$i1 = SELECT * FROM my_table;
$i2 = SELECT * FROM my_other_table;

$test_map = ($input) -> {
    RETURN YQL::Map($input, ($item) -> (AsStruct(Way($item) AS Data)))
};

PROCESS $i1, $i2 USING $test_map(TableRows());

Optimisation error:

<main>:12:17: Warning: It is not recommended to directly access s-expressions functions via YQL::
This mechanism is mostly intended for temporary workarounds or internal testing purposes, code: 4510
<main>: Error: Execution, code: 1060
    <main>:15:1: Error: Unexpected node in results: (
(let $1 (DataSource '"KqpReadRangesSource"))
(let $2 (KqpTable '"/Root/my_table" '"72057594046644480:40" '"" '1))
(let $3 '('"key" '"value"))
(let $4 (KqpRowsSourceSettings $2 $3 '() (Void) '()))
(let $5 (lambda '($12) (ToFlow $12)))
(let $6 (DqStage '((DqSource $1 $4)) $5 '('('"_logical_id" '611))))
(let $7 (DqCnUnionAll (TDqOutput $6 '"0")))
(let $8 (KqpTable '"/Root/my_other_table" '"72057594046644480:41" '"" '1))
(let $9 (KqpRowsSourceSettings $8 $3 '() (Void) '()))
(let $10 (DqStage '((DqSource $1 $9)) $5 '('('"_logical_id" '627))))
(let $11 (DqCnUnionAll (TDqOutput $10 '"0")))
(return (OrderedLMap (Mux '($7 $11)) (lambda '($13) (FlatMap $13 (lambda '($14) (Just (AsStruct '('"Data" (Way $14)))))))))
)