Please fix this ASAP. I have only started using Unity in any real capacity again in late 2019, and this issue seems to have popped up for me right around the time I updated to a 2020 version and switched my project to the URP, but I have seen others mention having this issue who were using the default renderer.

The quickest fix for me is to copy the contents of Default.wlt from Unity's folder in AppData over CurrentLayout-default.wlt in my projects library folder, but this fix only works for the amount of time Unity is open for the first launch. As soon as it closes and re-opens, it begins to fall apart.
First with NullReferenceExceptions to Unity UI elements, then later the inspector window will start to merge all of its different components over eachother, making modifying anything a major chore of minimizing every component just to see the contents of one, because the inspector is destroyed, can't even scroll in it with the mouse wheel anymore.

The next time it launches, it will run this infinite loop of being unable to fix itself.

Windows, Unity 2020.1.5f1.

Quoting banksysan_unity (the workaround worked for me)
"Copy one of the layouts from the default list in the editor directory into the Library folder overwriting CurrentLayout-default.dwlt.

i.e.

C:\Program Files\Unity\Hub\Editor\<Version>\Editor\Data\Resources\Layouts\2 by 3.wlt => …\Library\CurrentLayout-default.dwlt."

My path was different:
C:\Program Files\Unity\Editor\Data\Resources\Layouts\2 by 3.wlt
You have to rename whatever one you choose to CurrentLayout-default.dwlt, then copy to your Library in your project.

This also affects MacOS Catalina -- 10.15.6 (19G2021) // Unity 2020.1.5f1

run the following to fix
```bash
cd ~/Library/Preferences/Unity/Editor-5.x/Layouts/default
mv LastLayout.dwlt LastLayout.dwlt.bak
cd <project_dir>/Library
mv CurrentLayout-default.dwlt CurrentLayout-default.dwlt.bak
```

hope that helps :)

The workaround with copying over the content of the file after quitting (because the "quit" option apparently corrupts the file") works for me, but the problem keeps coming back, usually after a reboot.

My solution for now is to have a working CurrentLayout-default.dwlt handy in case it breaks again.

Solved!!
1-Go to the location where your games file is located and click it.
2-Go to Library.
3-There you find a file named CurrentLayout-default.dwlt open it with visual studio.
4-Now go to UnityHub and open your project.
5-When the "CANNOT LOAD EDITOR LAYOUT" notification appear click on load default
6-Now go back to visual studio and copy all the code
7-Then press the "Quit" button
8-Notice that the code in the visual studio project changed, delete all of it.
9-Finally paste the code that you've copied before and save the project.
Now go to Unity Hub and try open your project, it should work.
Credits to XEZRUNNER.

Had the same thing - after installing 2020.2 beta. It happened on both 2020.1 & 2020.2

IMAKHIIL's solution works for me. Restore factory defaults makes the right change to CurrentLayout-default.dwlt, but clicking Quit reverts the change back to the broken version(weird!). So you have to edit the file after clicking factory default but before clicking quit and copy the contents somewhere (clipboard is fine). Then Quit, then paste the factory default content back into the file and save it.

2020.2.0b1.2959 -- Same problem.

Xezrunner's workaround helped me tho:

"I managed to solve the window layout issue this way:
- I clicked on 'Load default layout' - the contents of CurrentLayout-default.dwlt reverted to the correct form that would work.
- I opened the file in Notepad++.
- It then returned to an empty (corrupt) layout file when clicking 'Quit'.
- Notepad++ now offered me to refresh the file, which I declined.
- I now saved the previous, correct file.

The project now opens."

Also occurs on 2020.1.6f1