How much disk space does a Fortnite update require?

I recently had the opportunity to install Fortnite on PC after playing for a year on GeForce Now. Everything is fine with the game except for the updates. For some reason, if, for example, the update weighs 2 GB, as it installs, the disk space starts to decrease to 60 GB and then returns to normal. I don't know if it's just my case or if it happened to someone else. Is there any way to fix this? I literally have about 90 GB free right now because I have other games. Any advice would be really helpful.