Default tray gone blank

Any explanations/ fixes?
This happened when I hit “B” to add a material.
(Materials, and many other features ARE checked in the default tray options)

No idea, have you tried restarting sketchup? Do you have more than one screen and have changed your setup recently? This is one of those time that seeing the whole screen rather than a crop might have helped.

Restarting it fixed it.
Thank you very much!