Problems with previews: missing, grey, green or black screen instead of video preview, slow previews

Possible solution 1

1. Update your operating system & Adobe products.
2. Update Animation Composer (open Mister Horse Product Manager and check if there is available update).
3. Quit all other applications that are not required to be running. For example we had reports that having "MSI After Burner" application running at the same time caused problems. We've also received reports about following applications: "RivaTuner", "GPU Tweak". 
4. Windows Only: Make sure to update your graphic card drivers. Use only drivers downloaded from your graphic card vendor (Nvidia, AMD), do not use 3rd party driver installers (like Driver Booster or similar).
5. Restart computer.

In our experience this issue is usually caused by bad drivers on Windows. On Macs usually the solution 2 below helps. 

Possible solution 2

Close all other extension panels. We had some reports that some extensions cause our previews to misbehave. This happens when other extension refreshes UI often or does some calculations while idle.

Possible solution 3

Reduce the size of the panel so it only displays 3x3 previews.