Filter Everything with ElasticPress

When using filter everything and elastic press I see using a query browser / debugger that there is second call after Main Query to “post” that takes around 3 seconds. It seems like all the filtering happens in the first call (and quick!), does anyone know what the second call could be? Or if it can be turned off / ignored? It doesn’t seem to be applying / sending the filter settings like the first call or anything like that.