Why does my code compile faster on nightly?

I have a big rust project with around 500 deps to compile. A week ago or so, I picked it up again and compiled it with the latest stable in release mode and had to wait about 25min. Approx 75% of the time was spend in the final step of the process where the actual binary is put together (where it says "(bin)" after the project name)

Because of that even an incremental build took about 18min.

I tried to solve it by updating all the deps and following some random advices that come up when you Google it. Nothing helped much.

After a while I thought that perhaps using the nightly compiler would help because who knows, perhaps there is some new speedy feature on the way. And tada, now my incremental build only takes <2min.

Does anybody know what could cause this?

Thanks in advance!