Fortnite fps drops without streaming?

I streamed fortnite 2 days ago at 780p 60fps and I had a constant 160fps in the game without 1 drop while streaming and today I only play fortnite without streaming and very often have fps drops why is that?

What kind of upload do you stream with? The best thing to do is to do an internet speed test.

What does that have to do with it? I have fps drops and my ping is perfect