Missing thumbnail on material browser

[stefanome]

When I click on the Paint tool and the Material Browser dialog pops up, there are no material defined. Here is what I see:

Why did the materials disappear?

How do I get them back?

I am using Revit 2021.1.2

[barthbradley · Accepted solution]

Slowly refreshing material thumbnails while opening the material browser in Revit 2021 | Revit Produ...

[stefanome]

Thank you. 

I had not realized that the materials are there, it's just a thumbnail problem.