At first, I couldn't find what the cause was but now I know it's the Package Manager. I had an editor layout saved that had the Package Manager as a tab and whenever I open the editor it just froze. After opening/upgrading another project from the alpha version that didn't have the package manager window open/docked it ran fine, but as soon as I opened the package Manager it froze. I opened the project multiple times and each time I open the Package Manager (or had it docked somewhere in the layout) it would freeze so I'm pretty sure it's the Package Manager. This happened as well in the alpha but I couldn't figure out the caused then. I could use the package manager in the alpha fine for some projects while others would freeze as soon as I opened them. So I didn't know this would be the cause at the time. In 2019.1 b1 every project I upgrade and open the Package Manager (or had it open and docked before upgrading) freezes the editor. New projects created in 2019.1 b1 don't have this problem. I can open the Package Manager fine as well as dock it and after reopening the editor it doesn't freeze. The editor only froze if I had a layout (made in 2018.3) with the Project Settings and or Preferences tabs docked in the layout and update. ( It only froze when I switched to those tabs though) So I had to delete the library and open the project again and switched to factory defaults (For the Layout) when the dialog option appears while the project is reopening. If I didn't switch to those tabs, everything worked fine. After upgrading other projects I just had to right click and close those tabs (not selecting/switching) then reopen them and they worked fine. Case number - 1124696 I dont have this problem in 2019.2 a4 so far. I checked with a few projects that followed this update chain 2018.3 -> 2019.1 b1 -> 2019.1 b2 -> 2019.2 a4. The issue only occurs in both 2019.1 versions.