API Platform version(s) affected: 2.6.0-alpha.1 + Symfony 5.2

Description
Following this tutorial with Symfony5.2 and latest APIPlatform 2.6.0-alpha.1 setting normalization context with custom data provider returns empty data for the fields marked with appropriate groups.

UPD: clearing cache didn't help

UPD 2
Somehow it does not react to manual setting normalizationContext groups either in camelcase "dailyStats:read" or with dash "daily-stats:read", or "dummystats:read".
But the data is displayed correctly only with default groups `"dailystats:read"``

For class defined like below I see only `totalVisitors`

/**
* @ApiResource(
*     normalizationContext={"groups"={"dummystats:read"}},
*     itemOperations={"get"},
*     collectionOperations={"get"}
* )
*/
class DailyStats
{
    /**
    * @Groups({"dummystats:read"})
    */
    public $date;
    
    /**
    * @Groups({"dailystats:read"})
    */
    public $totalVisitors;
}