The two queries in the following script give different answers:

~~~
CREATE TABLE t1(x INTEGER PRIMARY KEY, y);
CREATE UNIQUE INDEX t1y ON t1(y);
INSERT INTO t1 VALUES(111, 'AAA'),(222, 'BBB'),(333, 'CCC');
CREATE TABLE t2(z);
INSERT INTO t2 VALUES('BBB'),('AAA');
ANALYZE sqlite_schema;
INSERT INTO sqlite_stat1 VALUES('t1', 't1y','100 1');
ANALYZE sqlite_schema;

SELECT t1.x FROM t2 CROSS JOIN t1 WHERE t2.z = t1.y AND t1.x IN (111, 222);
SELECT t1.x FROM t2 CROSS JOIN t1 WHERE t2.z = t1.y AND +t1.x IN (111, 222);
~~~

The problem appears to have originated in check-in [](4a43430fd23f8835)
on 2020-09-30.  It was reported by
[Forum Post 0e5dcaae44](forum:/forumpost/0e5dcaae44)