I create a simple model in the Karma viewport. And I see that the final rendering time is sometimes 1 second, but sometimes when rotated by a few degrees, the time becomes 20-30-40 seconds. Then again 1 second, then again 30 seconds. Can someone explain what the trick is here? Neither the model nor the lighting changes, and the samples are very low.

I guess you should post the scene, so others can take a look....

Figured it out a bit. This is clearly a bug. If there is no camera in the scene, then karma behaves so strangely. If you add the camera, then everything is fine and works quickly.

HGaal
Figured it out a bit. This is clearly a bug. If there is no camera in the scene, then karma behaves so strangely. If you add the camera, then everything is fine and works quickly.

are you seeing both devices contribute when it takes longer, or just one? You can see the status next to the device name (idle, X%, compile, init, error)