White chocolate can be incredibly finicky when it comes to ganache. It's important to use a higher quality white chocolate that has a higher cocoa butter content (around 35%). Some good brands to use are Ghirardelli white chocolate bars, Guittard white chocolate bars or chips, Callebaut callets or Valrhona feves. Many brands of white chocolate chips lack the cocoa butter percentages that are good for melting. Chips are also formulated to hold their shape when baking so melting chips can be difficult, resulting in a texture that will not be silky and smooth, but sticky and thick.