My materials window shows only squares in one color in the topic I use the most. Some are still showing the material but other are not.
I already try to reboot sketch, but not reinstall because I don’t want to loose the new materials I created.
And today Setup crashed as I was downloading a new texture.
I don’t see any problem in your screenshot. Perhaps you can clearly describe the problem. The little squares at the bottom are not a materials collection. they are the Mac palette where you can drag and drop custom colors to use later.
Please correct you forum profile with the right information about operating system, etc. IF that information is correct it helps us help you. When it’s not, it makes helping you more difficult.