… Is anyone can explain this ?

Thank you

Linux?

The solution is here : https://www.sidefx.com/index.php?option=com_forum&Itemid=172&page=viewtopic&t=40972&view=next [sidefx.com]

Could you post your system specs, including OS, graphics card and graphics driver version? It's hard to say what might be the problem without that information (though it looks like a graphics driver problem).