To reproduce:
1. Open attached project
2. Open scene LightSocketTest. It contains a lens flare and a socket mesh collider that should cover the lens flare
3. Bug one - move the flare, it does not appear. To make it appear, set the ignore layers to nothing/everything until it appears. (Make sure it is outside the socket)
3. Select the Flare and make sure that it's ignore layers are so to ignore except the lightsocket layer
4. Enter play mode
5. Move the flare so that it's inside the socket - it does not disappear

Setting the ignore layers to none works, but it should also work if the lightsocket is the only one that's not ignored