After a couple of minutes making adjustments in LR develop a bright blue screen with a white perimeter and white diagonals flashes up and obscures the image. If I release the adjustment key it vanishes only to return the next time I try the adjustment. This is intermittent but once it has started the only answer is to close LR and start again. Any suggestions? Only seems to have happened since the last update.
The blue screen with a white X is usually an indication that the GPU optimization is not working correctly. Try turning it off:
Menu: / edit / preferences / performance / use graphics processor