Html5-apps built with -Webgl show just black screen on one android-tablet and work fine on another

Html5-apps built with -Webgl show just black screen on one android-tablet and work fine on another. It happens even with default Pirate Pig game. All browsers have webgl support. Everything else works. I know it because i have listened sound effects. It seems it depends on the tablet, and not on the browsers - I have tried different. Can anybody point me in the right direction to fix this?