Steps to reproduce the issue

Use $query->whereIn() in a frontend model, with an array with more than 1 item.
Sometimes only 1 row is returned.

Expected result

all rows for the array in the where in returned

Actual result

only some rows are returned

System information (as much as possible)

Database Type mysql
Database Version 5.6.49
Database Collation utf8_general_mysql500_ci
Database Connection Collation utf8mb4_general_ci
Database Connection Encryption None
Database Server Supports Connection Encryption No
PHP Version 7.4.11
Web Server Apache
WebServer to PHP Interface litespeed
Joomla! Version Joomla! 4.0.0-beta5-dev Development [ Mañana ] 15-September-2020 19:15 GMT
User Agent Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/86.0.4240.75 Safari/537.36

Additional comments

$query->whereIn('u.id', $users); - returns only 1 of 4 $users from the array

$query->where('u.id IN(' . implode(',', $db->quote($users)) . ')'); - works as expected and returns all 4 $users in the array