I upgraded the project from 2018.3.5f1 . I reset the packages to default because Timeline was yielding a bunch of errors.
Now i need to re-install the 2D Perfect Pixel camera for it to work like before, but every time i open package manager it freezes my whole editor.
Unity also uses about 13% of my CPU, but it's just frozen for a long time - i left it running for about 10 mins and no progress.

To reproduce:
- Download this project
- Open it with Unity 2019.1.0b4 (on Windows)
- Open package manager

Cannot reproduce in empty project
Cannot reproduce in 2018.3.5f1, 2019.1.0b1
Reproducible in 2019.1.0b2 and later and 2019.2.0a6