GraphQL query order entries by Lightswitch and DateTime field

I have an entries with the "highlighted" lightswitch that puts entry on top of the result list when enabled, also I need to sort items by post date. So, in the end there should be the following order: highlighted entries ordered by date, then other entries also ordered by date

I am using orderBy: "platformHighlighted DESC, postDate DESC" variable, however I see the postDate ordering is broken in the middle of the list

Is there something I do wrong in the query?

Thank you