MongoDB query is slow on first view runs, but then dramatically speeds up afterwards

My MongoDB Atlas collection has 1 million documents and about 10 indexes.

I have a query that has arbitrary filter conditions.

I notice that sometimes whenever I create a new set of filter conditions it runs really slowly in the first 4 or 5 runs, taking about 16 seconds to return. But then afterwards, it speeds up dramatically and only take about 1 or 2 seconds to return.

What explains?